Method for additive manufacturing with partial curing

ABSTRACT

A method of additive manufacturing (AM) includes dispensing a first building material formulation to form an outer region, and dispensing a second building material formulation to form an inner region, the outer region surrounding the inner region, the inner and outer regions being shaped to form a layer of the object; exposing the layer to a first curing condition, repeating the dispensing and the exposing to sequentially form a plurality of layers of the object and collectively exposing the plurality of layers to a second curing condition. The selections are such that the first building material formulation is hardened to a higher degree than the second building formulation. The outer regions form a hardened coating that at least partially encapsulates the inner regions. The second curing condition is other than the first curing condition and is selected to increase the degree that the inner region is hardened.

RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalPatent Application No. 62/738,041 filed on Sep. 28, 2018, the contentsof which are incorporated herein by reference in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to additivemanufacturing (AM), and, more particularly, but not exclusively, tonovel formulation systems usable in, and method parameters for AM.

Additive manufacturing (AM) is a technology enabling fabrication ofarbitrarily shaped structures directly from computer data via additiveformation steps. The basic operation of any AM system consists ofslicing a three-dimensional computer model into thin cross sections,translating the result into two-dimensional position data and feedingthe data to control equipment which fabricates a three-dimensionalstructure in a layerwise manner.

Additive manufacturing entails many different approaches to the methodof fabrication, including three-dimensional (3D) printing such as 3Dinkjet printing, electron beam melting, stereolithography, selectivelaser sintering, laminated object manufacturing, fused depositionmodeling and others.

Some 3D printing processes, for example, 3D inkjet printing, are beingperformed by a layer by layer inkjet deposition of building materials.Thus, a building material is dispensed from a dispensing head having aset of nozzles to deposit layers on a supporting structure. Depending onthe building material, the layers may then be cured or solidified.Curing may be by exposure to a suitable condition, and optionally byusing a suitable device.

The building material includes an uncured model material (also referredto as “uncured modeling material” or “modeling material formulation”),which is selectively dispensed to produce the desired object, and mayalso include an uncured support material (also referred to as “uncuredsupporting material” or “support material formulation”) which providestemporary support to specific regions of the object during building andassures adequate vertical placement of subsequent object layers. Thesupporting structure is configured to be removed after the object iscompleted.

In some known inkjet printing systems, the uncured model material is aphotopolymerizable or photocurable material that is cured, hardened orsolidified upon exposure to ultraviolet (UV) light after it is jetted.The uncured model material may be a photopolymerizable materialformulation that has a composition which, after curing, gives a solidmaterial with mechanical properties that permit the building andhandling of the three-dimensional object being built. The materialformulation may include a reactive (curable) component and aphoto-initiator. The photo-initiator may enable at least partialsolidification of the uncured support material by curing with the sameUV light applied to form the model material. The solidified material maybe rigid, or may have elastic properties. The support material isformulated to permit fast and easy cleaning of the object from itssupport. The support material may be a polymer, which is water-solubleand/or capable of swelling and/or breaking down upon exposure to aliquid solution, e.g. water, alkaline or acidic water solution. Thesupport material formulation may also include a reactive (curable)component and a photo-initiator similar to that used for the modelmaterial formulation.

In order to be compatible with most of the commercially-available printheads utilized in a 3D inkjet printing system, the uncured buildingmaterials are known to feature the following characteristics: arelatively low viscosity (e.g., Brookfield viscosity of up to 50 cps, orup to 35 cps, preferably from 8 to 25 cps) at a working (e.g., jetting)temperature; surface tension from about 25 to about 55 Dyne/cm,preferably from about 25 to about 40 Dyne/cm; and a Newtonian liquidbehavior and high reactivity to a selected curing condition, to enablefast solidification of the jetted layer upon exposure to a curingcondition, of no more than 1 minute, preferably no more than 20 seconds.

The hardened modeling material which forms the final object typicallyexhibits heat deflection temperature (HDT) which is higher than roomtemperature, in order to assure its usability. Desirably, the hardenedmodeling material exhibits HDT of at least 35° C. For an object to bestable at variable conditions, a higher HDT is known to be desirable. Inmost cases, it is also desirable that the object exhibits relativelyhigh Izod Notched impact, e.g., higher than 50 or higher than 60 J/m.

Various three-dimensional printing techniques exist and are disclosedin, e.g., U.S. Pat. Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334,6,863,859, 7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,500,846,7,991,498 and 9,031,680 and U.S. Published Application No. 20160339643,all by the same Assignee, and being hereby incorporated by reference intheir entirety.

Several additive manufacturing processes, including three-dimensionalinkjet printing, allow additive formation of objects using more than onemodeling material, also referred to as “multi-material” AM processes.For example, U.S. patent application having Publication No.2010/0191360, of the present Assignee, discloses a system whichcomprises a solid freeform fabrication apparatus having a plurality ofprint heads, a building material supply apparatus configured to supply aplurality of building materials to the fabrication apparatus, and acontrol unit configured for controlling the fabrication and supplyapparatus. The system has several operation modes. In one mode, allprint heads operate during a single building scan cycle of thefabrication apparatus. In another mode, one or more of the print headsis not operative during a building scan cycle or part thereof.

In a 3D inkjet printing process such as Polyjet™ (Stratasys® Ltd.,Israel), the building material is selectively jetted from one or moreinkjet print heads and/or nozzles and deposited onto a fabrication trayin consecutive layers according to a pre-determined configuration asdefined by a software file.

U.S. Pat. No. 9,227,365, by the present assignee, discloses methods andsystems for solid freeform fabrication of shelled objects, constructedfrom a plurality of layers and a layered core constituting core regionsand a layered shell constituting envelope regions. This is also referredto as digital ABS™, or D-ABS™.

The Polyjet™ technology allows control over the position and compositionof each voxel (volume pixel), which affords enormous design versatilityand digital programming of multi-material structures. Other advantagesof the Polyjet™ technology is the very high printing resolution, up to14 μm layer height, and the ability to print multiple materialssimultaneously, in a single object. This multi-material 3D printingprocess often serves for fabrication of complex parts and structuresthat are comprised of elements having different stiffness, performance,color or transparency. New range of materials, programmed at the voxellevel, can be created by the PolyJet™ printing process, using only fewstarting materials.

International Patent Application Publication No. WO 2013/128452, by thepresent Assignee, discloses a multi-material approach which involvesseparate jetting of two components of a cationic polymerizable systemand/or a radical polymerizable system, which intermix on the printingtray, leading to a polymerization reaction similar to pre-mixing of thetwo components before jetting, while preventing their earlypolymerization on the inkjet head nozzle plate.

Current PolyJet™ technology offers the capability to use a range ofcurable (e.g., polymerizable) materials that provide polymeric materialsfeaturing a variety of properties, ranging, for example, from stiff andhard materials (e.g., curable formulations marketed as the Vero™ Familymaterials) to soft and flexible materials (e.g., curable formulationsmarketed as the Tango™ and Agilus families), and including also objectsmade using Digital ABS, which contain a multi-material made of twostarting materials (e.g., RGD515™ & RGD535/531™), and simulateproperties of engineering plastic. Most of the currently practicedPolyJet™ materials are curable materials which harden or solidify uponexposure to radiation, mostly UV radiation and/or heat, with the mostpracticed materials being acrylic-based materials.

Acrylic-based materials typically feature non-optimal thermal stability(resistance to thermal deformation). For example, acrylic-basedmaterials such as multi-functional acrylic materials, which feature,when hardened, Tg above 200° C., exhibit high volume shrinkage whichoften results in curling and/or deformation of the printed object.

Curable materials which feature low volume shrinkage when hardenedinclude, for example, epoxides, polyurethanes, polyamides, benzoxazineand cyanate esters (CE). However, most of these materials are notcompatible with the PolyJet™ methodology due to technologicalrestrictions such as high viscosity of the modeling formulationcontaining same at the inkjet printing heads' working temperature,instability, and toxicity.

Additional background art includes WO 2009/013751; WO 2016/063282; WO2016/125170; WO 2017/134672; WO 2017/134673; WO 2017/134674; WO2017/134676; WO 2017/068590; WO 2017/187434; WO 2018/055521; and WO2018/055522, all to the present assignee.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided a system and method for fabricating objects with atleast one model material that is maintained in a partially solidified ornot solidified state throughout the additive manufacturing process. Insome example embodiments, the system and method additionally includes apost treatment process during which the partially solidified or notsolidified material may be further solidified. In some exampleembodiments, the system is configured to solidify the object in a dualstage hardening process. The dual stage hardening process may includepartial solidification of the object during the AM process to produce agreen body object followed by post (e.g., thermal) treatment at the endof the AM process to complete the solidifying process. During the AMprocess, potential smearing of the partially solidified printed pixelsmay be avoided by fully solidifying at least a portion of the object.Optionally, the portion of the object that is fully solidified maydefine a relatively hard shell or relatively hard coating (a solidifiedshell or coating) that forms an exterior of the object in which thepartially cured material is contained. In some example embodiments, thepartially cured material has a liquid to jelly-like consistency.

According to some example embodiments, the system and method isconfigured to reduce object curling or deformation that result fromvolume shrinkage of materials during curing. Optionally, the system andmethod may enable printing with materials that undergo substantialshrinking and/or have a relatively high heat distortion temperature(HDT), e.g., have an HDT above 50° C. or above 70° C.

According to some example embodiments, the system and method isconfigured to improve degree of transparency of the material forming theobject. In some additional example embodiments, the system and method isapplied to manufacture objects with a higher throughput.

According to an aspect of some embodiments of the present inventionthere is provided a method of manufacturing a three-dimensional objectvia additive manufacturing (AM), the method comprising:

dispensing a first building material formulation to form an outerregion, and dispensing a second building material formulation to form aninner region, the outer region surrounding the inner region, the innerand outer regions being shaped to form a layer of the object; and

exposing the layer to a first curing condition, wherein the first andthe second building material formulations and the first curing conditionare selected such that upon the exposing, the first building materialformulation is hardened to a higher degree than the second buildingformulation;

repeating the dispensing and the exposing to the first curing conditionto sequentially form a plurality of layers of the object, wherein theouter regions form a hardened coating that at least partiallyencapsulates the inner regions; and

collectively exposing the plurality of layers to a second curingcondition, wherein the second curing condition is other than the firstcuring condition and wherein the second curing condition is selected toincrease the degree that the inner region is hardened.

According to some of any of the embodiments described herein, the firstand second building material formulations and the first curing conditionare selected such that upon the exposing to the first curing condition,a change in a hardening parameter of the first formulation is higherthan a change in a hardening parameter of the second formulation by atleast 2-folds.

According to some of any of the embodiments described herein, thehardening parameter is viscosity and/or loss tangent.

According to some of any of the embodiments described herein, the firstand second building material formulations and the first curing conditionare selected such that upon the exposing to the first curing condition,a hardening kinetic parameter of the first formulation is higher than ahardening kinetic parameter of the second formulation by at least2-folds.

According to some of any of the embodiments described herein, thehardening kinetic parameter is a rate of a change in a viscosity or arate of a change in a loss tangent.

According to some of any of the embodiments described herein, the firstand the second building material formulations and the first curingcondition are selected such that upon the exposing to the first curingcondition, a hardening degree of the first building material formulationis at least 70% and a hardening degree of the second building materialformulation is no more than 50%.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable material and atleast one of the first and the second building material formulationscomprises an initiator for promoting hardening of the second curablematerial, and wherein the initiator is inactive or is partially activetowards the hardening upon exposure to the first curing condition.

According to some of any of the embodiments described herein, a totalamount of the initiator in the at least one of the first and secondbuilding material formulations is less than 50%, or less than 30%, byweight, of an amount of the initiator required for promoting hardeningof at least 70% of the second curable material upon exposure to thefirst curing condition.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises at least two sub-formulations Aand B, each comprising the second curable material, wherein an amount ofthe initiator in sub-formulation A is higher by at least 100% of anamount of the initiator in sub-formulation B, and wherein a weight ratioof sub-formulations A and B is lower than 0.5.

According to some of any of the embodiments described herein, dispensingthe second building formulation is such that the sub-formulation A isdithered within the inner region.

According to some of any of the embodiments described herein, the firstbuilding material formulation comprises a first curable material and aninitiator for promoting hardening of the first curable material, andwherein the initiator is active towards promoting the hardening uponexposure to the first curing condition.

According to some of any of the embodiments described herein, the firstcuring condition comprises irradiation.

According to some of any of the embodiments described herein, theirradiation is UV-irradiation.

According to some of any of the embodiments described herein, the firstbuilding material formulation comprises a first curable material whichis a UV curable material, and a photo-initiator in an amount sufficientfor promoting hardening of at least 70% of the first building materialformulation upon exposure to the first curing condition.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable material whichis a UV curable material, and a photo-initiator in an amount thatpromotes hardening of no more of 50% of the second building materialformulation upon exposure to the first curing condition.

According to some of any of the embodiments described herein, the secondbuilding material formulation hardens upon exposure to heat energy(e.g., application of heat energy).

According to some of any of the embodiments described herein, at leastone of the first and second building material formulations provides atransparent hardened material.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a heat distortion temperature (HDT) above asteady state temperature of the plurality of layers during the AMprocess.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a glass transition temperature (Tg) above asteady state temperature of the plurality of layers during the AMprocess.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a heat distortion temperature (HDT) above 70°C.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a glass transition temperature (Tg) above 70°C.

According to some of any of the embodiments described herein, the firstbuilding material formulation comprises a first curable materialfeaturing, when hardened, a heat distortion temperature (HDT) below asteady state temperature of the plurality of layers during the AMprocess.

According to some of any of the embodiments described herein, the firstbuilding material formulation comprises a first curable materialfeaturing, when hardened, a glass transition temperature (Tg) below asteady state temperature of the plurality of layers during the AMprocess. According to some of any of the embodiments described herein,the first building material formulation comprises a first curablematerial featuring, when hardened, a heat distortion temperature (HDT)below 70° C.

According to some of any of the embodiments described herein, the firstbuilding material formulation comprises a first curable materialfeaturing, when hardened, a glass transition temperature (Tg) below 70°C.

According to some of any of the embodiments described herein, thecoating is configured to have a thickness that is less than 1 mm.

According to an aspect of some embodiments of the present inventionthere is provided a three-dimensional object obtainable by the method asdescribed herein in any of the respective embodiments and anycombination thereof.

According to an aspect of some embodiments of the present inventionthere is provided a green body obtainable by the method as describedherein in any of the respective embodiments and any combination thereof,before exposing the layers to the second curing condition.

According to an aspect of some embodiments of the present inventionthere are provided kits comprising the first and second formulations asdescribed herein in any of the respective embodiments.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings (includingimages). With specific reference now to the drawings in detail, it isstressed that the particulars shown are by way of example and forpurposes of illustrative discussion of embodiments of the invention. Inthis regard, the description taken with the drawings makes apparent tothose skilled in the art how embodiments of the invention may bepracticed.

In the drawings:

FIG. 1 is a simplified block diagram of an example ink-jet printingsystem for three dimensional printing for use with some exampleembodiments;

FIGS. 2A-C are schematic illustrations of another additive manufacturingsystem according to some embodiments of the invention;

FIGS. 3A-3C are schematic illustrations of printing heads according tosome embodiments of the present invention;

FIGS. 4A and 4B are schematic illustrations demonstrating coordinatetransformations according to some embodiments of the present invention;

FIGS. 5A and 5B are simplified schematic drawings of a cross sectionalview of an object fabricated with a core filled with a non-reactivebuilding material formulation encompassed by a shell formed with areactive building material formulation and a top view of a single layerof the object respectively, both in accordance with some exampleembodiments;

FIGS. 6A and 6B are simplified schematic drawings of a cross sectionalview of an object fabricated with a core filled with non-reactivebuilding material formulation, dithered with a reactive buildingmaterial formulation and encompassed by another reactive buildingmaterial formulation and a top view of a single layer of the objectrespectively, both in accordance with some example embodiments;

FIG. 7 is a simplified schematic drawing of a cross-sectional view of anobject encapsulated in support material in accordance with some exampleembodiments;

FIG. 8 is a simplified flow chart of an example method to fabricate anobject with reduced asymmetrical shrinking in accordance with someexample embodiments;

FIG. 9 is a simplified block diagram of an example ink-jet printingsystem for three dimensional printing in accordance with some exampleembodiments;

FIG. 10 is an example pixel map for a curling bar model to be printedbased on some example embodiments;

FIGS. 11A and 11B are images of example objects printed with cyanateester-containing formulation system in accordance with some exampleembodiments;

FIGS. 11C and 11D are images of a curling bar manufactured by AM as agreen body object and hardened in a thermal post process respectivelyand in accordance with some example embodiments;

FIGS. 12A and 12B are pairs of example curling bar models printed withacrylic-based formulation that provide high HDT material in accordancewith some example embodiments;

FIGS. 13A and 13B are example curling bar models printed withBMI-containing formulation in accordance with some example embodiments;and

FIG. 14 is an image of example transparent objects printed withacrylic-based formulations in accordance with some example embodiments.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to additivemanufacturing (AM), and, more particularly, but not exclusively, tonovel formulation systems usable in, and method parameters for AM.

The present inventors have designed and successfully practiced a methodof additive manufacturing a three-dimensional object featuring improvedproperties while overcoming limitations associated with various modelmaterials, as is discussed in further detail hereinafter. Hereinthroughout, the phrases “building material formulation”, “uncuredbuilding material”, “uncured building material formulation”, “buildingmaterial” and other variations therefore collectively describe thematerials that are dispensed to sequentially form the layers, asdescribed herein. This phrase encompasses uncured materials dispensed soas to form the object, namely, one or more uncured modeling materialformulation(s), and uncured materials dispensed so as to form thesupport, namely uncured support material formulations.

Herein throughout, the term “object” describes a final product of theadditive manufacturing. This term refers to the product obtained by amethod as described herein, after removal of the support material, ifsuch has been used as part of the uncured building material, and afterpost treatment (e.g., exposure to second curing condition as describedherein). The object therefore typically consists (at least 95 weightpercent) of a cured (hardened, solidified) modeling material or acombination of two or more modeling materials. In some applications, theobject includes, in at least a portion thereof, partially cured and/oruncured modeling material(s).

The term “object” as used herein throughout refers to a whole object ora part thereof.

Herein throughout, the phrase “cured modeling material” which is alsoreferred to herein as “hardened” or solidified” modeling materialdescribes the part of the building material that forms the object, asdefined herein, upon exposing the dispensed building material to acuring condition (and optionally post-treatment), and, optionally, if asupport material has been dispensed, removal of the cured supportmaterial, as described herein. The hardened modeling material can be asingle hardened material or a mixture of two or more hardened materials,depending on the modeling material formulations used in the method, asdescribed herein.

The phrases “cured modeling material”, “hardened modeling material”,“solidified modeling material” or “cured/hardened/solidified modelingmaterial formulation” can be regarded as a cured building materialwherein the building material consists only of a modeling materialformulation (and not of a support material formulation). That is, thisphrase refers to the portion of the building material, which is used toprovide the final object.

Herein throughout, the phrase “modeling material formulation”, which isalso referred to herein interchangeably as “modeling formulation”,“modeling material” “model material” or simply as “formulation”,describes a part or all of the uncured building material which isdispensed so as to form the object, as described herein. The modelingmaterial formulation is an uncured modeling formulation (unlessspecifically indicated otherwise), which, upon exposure to a conditionthat effects curing, may form the object or a part thereof.

In some embodiments of the present invention, a modeling materialformulation is formulated for use in three-dimensional inkjet printingand is able to form a three-dimensional object on its own, i.e., withouthaving to be mixed or combined with any other substance.

An uncured building material can comprise one or more modeling materialformulations, and can be dispensed such that different parts of theobject are made, upon being hardened, of different cured modelingformulations, and hence are made of different hardened (e.g., cured)modeling materials or different mixtures of hardened (e.g., cured)modeling materials.

The final three-dimensional object is made of the modeling material or acombination of modeling materials or a combination of modelingmaterial/s and support material/s or modification thereof (e.g.,following curing). All these operations are well-known to those skilledin the art of solid freeform fabrication.

In some exemplary embodiments of the invention, an object ismanufactured by dispensing a building material that comprises two ormore different modeling material formulations, each modeling materialformulation from a different dispensing head and/or nozzle of the inkjetprinting apparatus. The modeling material formulations are optionallyand preferably concurrently deposited during the same pass of theprinting heads. The modeling material formulations and/or combination offormulations within a layer are selected according to the desiredproperties of the object and according to the method parametersdescribed herein.

According to some of any of the embodiments described herein, each ofthe modeling material formulations comprises one or more curablematerials.

Herein throughout, a “curable material” or a “solidifiable material” isa compound (e.g., monomeric or oligomeric or polymeric compound) which,when exposed to a curing condition (e.g., curing energy), as describedherein, solidifies or hardens to form a cured modeling material asdefined herein. Curable materials are typically polymerizable materials,which undergo polymerization and/or cross-linking when exposed to asuitable energy source. A curable or solidifiable material is typicallysuch that its viscosity increases by at least one order of magnitudewhen it is exposed to a curing condition.

In some of any of the embodiments described herein, a curable materialcan be a monomer, an oligomer or a short-chain polymer, each beingpolymerizable as described herein.

In some of any of the embodiments described herein, when a curablematerial is exposed to curing energy (e.g., radiation), it polymerizesby any one, or combination, of chain elongation and cross-linking.

In some of any of the embodiments described herein, a curable materialis a monomer or a mixture of monomers which can form a polymericmodeling material upon a polymerization reaction, when exposed to acuring condition at which the polymerization reaction occurs. Suchcurable materials are also referred to herein as monomeric curablematerials.

In some of any of the embodiments described herein, a curable materialis an oligomer or a mixture of oligomers which can form a polymericmodeling material upon a polymerization reaction, when exposed to acuring condition at which the polymerization reaction occurs. Suchcurable materials are also referred to herein as oligomeric curablematerials.

In some of any of the embodiments described herein, a curable material,whether monomeric or oligomeric, can be a mono-functional curablematerial or a multi-functional curable material.

Herein, a mono-functional curable material comprises one functionalgroup that can undergo polymerization when exposed to a curing condition(e.g., curing energy).

A multi-functional curable material comprises two or more, e.g., 2, 3, 4or more, functional groups that can undergo polymerization when exposedto a curing condition. Multi-functional curable materials can be, forexample, di-functional, tri-functional or tetra-functional curablematerials, which comprise 2, 3 or 4 groups that can undergopolymerization, respectively. The two or more functional groups in amulti-functional curable material are typically linked to one another bya linking moiety, as defined herein. When the linking moiety is anoligomeric moiety, the multi-functional group is an oligomericmulti-functional curable material.

Exemplary curable materials that are commonly used in additivemanufacturing and in some of the present embodiments are acrylicmaterials.

Herein throughout, the term acrylic materials collectively encompassmaterials bearing one or more acrylate, methacrylate, acrylamide and/ormethacrylamide group(s).

The curable materials included in the first and second formulationsdescribed herein may be defined by the properties provided by eachmaterial, when hardened. That is, the materials may be defined byproperties of a material formed upon exposure to a curing condition, forexample, upon polymerization. These properties (e.g., Tg, HDT), are of apolymeric material formed upon curing any of the described curablematerials alone.

As used herein, each of the terms “curing” and “hardening” describes aprocess in which a formulation is hardened. These terms encompasspolymerization of monomer(s) and/or oligomer(s) and/or cross-linking ofpolymeric chains (either of a polymer present before curing or of apolymeric material formed in a polymerization of the monomers oroligomers). The product of a curing reaction or of a hardening istherefore typically a polymeric material and in some cases across-linked polymeric material.

Partial curing or hardening as used herein encompasses a curing orhardening process that does not reach completion, that is, for example,a process that is effected up to a hardening degree, as definedhereinafter, which is less than 100%, less than 90%, or less than 80%.Material that is partially cured may stay in a liquid-jelly state.Complete curing or hardening as used herein is curing or hardening to adegree of at least 80%, or at least 90%, or of about 100%, for example,a curing or hardening process that results in a solidified material.

A “degree of hardening” as used herein represents the extent at whichcuring is effected, that is, the extent at which curable materialsunderwent polymerization and/or cross-linking. When a curable materialis a polymerizable material, this phrase encompasses both a mol % of thecurable materials in a formulation that underwent polymerization and/orcross-linking, upon exposure to a curing condition; and/or the degree atwhich polymerization and/or cross-linking was effected, for example, thedegree of chain elongation and/or cross-linking. Determining a degree ofpolymerization can be performed by methods known to those skilled in theart.

A “green body object” as used herein is an object formed by an AMprocess that has at least a portion that only been partially hardened orsolidified and requires additional hardening to obtain a fullysolidified object.

Herein, the phrase “a condition that affects curing” or “a condition forinducing curing”, which is also referred to herein interchangeably as“curing condition” or “curing inducing condition” describes a conditionwhich, when applied to a formulation that contains a curable material,induces polymerization of monomer(s) and/or oligomer(s) and/orcross-linking of polymeric chains. Such a condition can include, forexample, application of a curing energy, as described hereinafter, tothe curable material(s), and/or contacting the curable material(s) withchemically reactive components such as catalysts, co-catalysts, andactivators.

When a condition that induces curing comprises application of a curingenergy, the phrase “exposing to a curing condition” means that thedispensed layers are exposed to the curing energy and the exposure istypically performed by applying a curing energy to the dispensed layers.

A “curing energy” typically includes application of radiation orapplication of heat.

The radiation can be electromagnetic radiation (e.g., ultraviolet orvisible light), or electron beam radiation, or ultrasound radiation ormicrowave radiation, depending on the materials to be cured. Theapplication of radiation (or irradiation) is effected by a suitableradiation source. For example, an ultraviolet or visible or infrared orXenon lamp can be employed, as described herein. A curable material orsystem that undergoes curing upon exposure to radiation is referred toherein interchangeably as “photopolymerizable” or “photoactivatable” or“photocurable”.

In some of any of the embodiments described herein, a curable materialis a photopolymerizable material, which polymerizes or undergoescross-linking upon exposure to radiation, as described herein, and insome embodiments the curable material is a UV-curable material, whichpolymerizes or undergoes cross-linking upon exposure to UV-visradiation, as described herein.

In some embodiments, a curable material as described herein includes apolymerizable material that polymerizes via photo-induced radicalpolymerization.

When the curing energy comprises heat, the curing is also referred toherein and in the art as “thermal curing” and comprises application ofthermal energy. Applying thermal energy can be effected, for example, byheating a receiving medium onto which the layers are dispensed or achamber hosting the receiving medium, as described herein. In someembodiments, the heating is effected using a resistive heater.

In some embodiments, the heating is affected by irradiating thedispensed layers by heat-inducing radiation. Such irradiation can beeffected, for example, by means of an IR lamp or Xenon lamp, operated toemit radiation onto the deposited layer.

A curable material or system that undergoes curing upon exposure to heatis referred to herein as “thermally-curable” or “thermally-activatable”or “thermally-polymerizable”.

Some curable materials can harden via thermal and/or photo-inducedcuring.

In some of any of the embodiments described herein, the method of thepresent embodiments uses a formulation system, which comprises two ormore building material formulations (e.g., two or more modeling materialformulations), which are dispensed and exposed to a curing conditionsuch that at least one of the building material formulations is onlypartially cured or not cured during the AM process. Optionally, curingof the object may be completed in a post treatment process, e.g. bythermal curing or by maintaining the object in environmental conditionsfor a defined period of time, e.g. exposing the object to roomtemperature for a pre-determined period of time (a pre-defined number ofhours). According to some example embodiments, the system may include afirst building material formulation (also referred to hereininterchangeably as a first modeling material formulation or as areactive formulation) which includes one or more curable materials andan initiator that promotes hardening of the curable materials in theformulation when exposed to a curing condition (a first curingcondition) and a second building material formulation (also referred toherein interchangeably as a second modeling material formulation or as anon-reactive formulation) includes curable material(s) without aninitiator or with an initiator that is inactive or is partially activein promoting hardening of the curable material(s) when exposed to thecuring condition (e.g., the first curing condition).

In some example embodiments, portions of the object that are configuredto be partially cured or not cured are formed with the second buildingmaterial formulation and portions of the object configured to be fullycured over the AM process are formed with the first building materialformulation. In some example embodiments, the degree that the portion iscured may be controlled based on controllably doping a portion of theobject that is configured for partial or no curing with the firstbuilding material formulation or with another reactive formulation. Thedegree of doping may define the degree of curing.

According to some example embodiments, the AM method includes forming acore of the object with the second building (e.g., modeling) materialformulation and a shell or surface of the object with the first building(e.g., modeling) material formulation. Optionally, the core may befurther cured in the post treatment process, by exposure to a secondcuring condition (e.g., thermal curing or by exposing the object to roomtemperature for a defined period of time).

In some example embodiments, the system and method is applied to preventcurling or deformation of objects during AM. In some exampleembodiments, the system and method is applied to improve transparency oftransparent model materials. Photo-initiators may add an undesired tintto transparent model materials. Optionally, by reducing concentration ofthe photo-initiators the tinting may be significantly reduced oravoided. In some example embodiments, the system and method is appliedto improve throughput. AM with the second building (e.g., modeling)material formulation may reduce the temperature buildup over the AMprocess. Typically, the scanning speed in the AM process is limited dueto the temperature buildup since it is generally desired to maintain theobject being built at a defined range of temperatures to reduce internalstress leading to deformations. Based on the reduced temperatureachieved, the speed of the scanning and the throughput may be increased.

A disadvantage of only partially curing the material during the AMprocess is that it may result in smearing of the printed pixels andtherefore in poor printing quality. According to some exampleembodiments, this disadvantage is avoided by fully curing a portion ofthe object during the AM process and partially curing or not curinganother portion(s).

In some example embodiments, the portion that is fully cured is an outerportion of the object, e.g. a perimeter of a layer of the object and theportion that is partially cured is an inner portion of the object, e.g.an inner portion of the layer of the object encompassed by the perimeterof the layer. Optionally, the outer portion forms a shell of the objectbeing printed and the inner portion that is partially cured or not curedforms a core of the object being printed. In some embodiments, the shellenvelops the core. In some embodiments, the core is at least partiallyenveloped by the shell. Optionally, the shell may be a thin coating ofone printed voxel thickness or may be a coating of 0.1 mm-2 mmthickness, e.g. 0.15 mm-0.3 mm thickness or 0.3 mm. The thickness mayvary based on the size and shape of the object being printed and may attimes be thicker than 2 mm.

For purposes of better understanding of some embodiments of the presentinvention, as illustrated in FIGS. 5A-14 of the drawings, reference isfirst made to the construction and operation of an ink-jet printingsystem for three dimensional printing as illustrated in FIGS. 1-4B.

A representative and non-limiting example of an inkjet printing system100 suitable for AM of an object 112 according to some embodiments ofthe present invention is illustrated in FIG. 1. Inkjet printing system100 may include inkjet printer 114 having a plurality of dispensingheads 116. Each head preferably includes an array of nozzles 122 throughwhich a liquid building material is dispensed via inkjet technology.Optionally and preferably a building material supply system or apparatus130 contains the building material containers or cartridges and suppliesa plurality of building material formulations to dispensing heads 116during printing. Each dispensing head 116 may be designated fordispensing one or more types of model material for forming object 112and may also be designated for dispensing one or more types of supportmaterial for forming supporting structure 115 for object 112.Optionally, one dispensing head 116 may dispense a first buildingmaterial formulation via a first set of nozzles in array 122 and asecond building material formulation via a second set of nozzles inarray 122. Although, in the representative example of FIG. 1, fourdispensing heads 116 are illustrated, it is contemplated that inkjetprinter 114 may optionally include fewer or more dispensing heads 116.

Inkjet printer 114 may also include a solidification system 124, e.g.hardening device, which can include any device configured to emit light,heat or the like and optionally and preferably harden one or more of themodeling material and the support material. For example, solidificationsystem 124 may include an ultraviolet (UV) lamp that may cure orotherwise solidify the modeling material and optionally the supportmaterial. In some exemplary embodiments, inkjet printer 114 furtherincludes a leveling device 132, e.g. a roller. Leveling device 132 maybe configured to straighten, flatten and/or establish a defined layerthickness of a current layer prior to formation of the successive layerthereon.

Dispensing heads 116, solidification system 124 and leveling device 132may be mounted on a frame or block 128 of inkjet printer 114 which ispreferably operative to reciprocally move over a tray 180, which servesas the working surface. In some embodiments, solidification system 124and leveling devices 132 are mounted in block 128 such that they followin the wake of dispensing heads 116 to at least partially solidify(e.g., cure) the materials just dispensed by the dispensing heads.Optionally, tray 180 is configured to move in one or more directions inwhich block 128 is stationary.

A computerized controller 152 controls fabrication with inkjet printer114 and optionally and preferably also controls supply system 330.Controller 152 typically includes one or more electronic circuitsconfigured to perform the controlling operations. Controller 152preferably communicates with a data processor 154 which transmitsdigital data pertaining to fabrication instructions based on computerobject data, e.g., a CAD configuration represented on a computerreadable medium in any of the aforementioned formats (e.g., STL).Typically, controller 152 controls the voltage applied to eachdispensing head or nozzle array and the temperature of the buildingmaterial in the respective printing head.

Once the manufacturing data is loaded to controller 152 it can operatewithout user intervention. In some embodiments, controller 152 receivesadditional input from the operator, e.g., using data processor 154 orusing a user interface 106, e.g. a display with a keyboard, a touchscreen and the like, communicating with controller 152. For example,controller 152 can receive, as additional input, one or more buildingmaterial types and/or attributes, such as, but not limited to, color,characteristic distortion and/or transition temperature, viscosity,electrical property, magnetic property. Other attributes and groups ofattributes are also contemplated.

Another representative and non-limiting example of a system 101 suitablefor AM of an object according to some embodiments of the presentinvention is illustrated in FIGS. 2A-2C. FIGS. 2A-2C illustrate a topview (FIG. 2A), a side view (FIG. 2B) and an isometric view (FIG. 2C) ofsystem 101.

In the present embodiments, system 101 comprises a tray 180 and aplurality of inkjet printing heads 116, each having a plurality ofseparated nozzles. Tray 180 can have a shape of a disk or it can beannular. Non-round shapes are also contemplated, provided they can berotated about a vertical axis.

Tray 180 and heads 116 are optionally and preferably mounted such as toallow a relative rotary motion between tray 180 and heads 116. This canbe achieved by (i) configuring tray 180 to rotate about a vertical axis14 relative to heads 116, (ii) configuring heads 116 to rotate aboutvertical axis 14 relative to tray 180, or (iii) configuring both tray180 and heads 116 to rotate about vertical axis 14 but at differentrotation velocities (e.g., rotation at opposite direction). While theembodiments below are described with a particular emphasis toconfiguration (i) wherein the tray is a rotary tray that is configuredto rotate about vertical axis 14 relative to heads 116, it is to beunderstood that the present application contemplates also configurations(ii) and (iii). Any one of the embodiments described herein can beadjusted to be applicable to any of configurations (ii) and (iii), andone of ordinary skills in the art, provided with the details describedherein, would know how to make such adjustment.

In the following description, a direction parallel to tray 180 andpointing outwardly from axis 14 is referred to as the radial directionr, a direction parallel to tray 180 and perpendicular to the radialdirection r is referred to herein as the azimuthal direction φ, and adirection perpendicular to tray 180 is referred to herein is thevertical direction z.

The term “radial position,” as used herein, refers to a position on orabove tray 180 at a specific distance from axis 14. When the term isused in connection to a printing head, the term refers to a position ofthe head which is at specific distance from axis 14. When the term isused in connection to a point on tray 180, the term corresponds to anypoint that belongs to a locus of points that is a circle whose radius isthe specific distance from axis 14 and whose center is at axis 14.

The term “azimuthal position,” as used herein, refers to a position onor above tray 180 at a specific azimuthal angle relative to apredetermined reference point. Thus, radial position refers to any pointthat belongs to a locus of points that is a straight line forming thespecific azimuthal angle relative to the reference point.

The term “vertical position,” as used herein, refers to a position overa plane that intersect the vertical axis 14 at a specific point.

Tray 180 serves as a supporting structure for three-dimensionalprinting. The working area on which one or objects are printed istypically, but not necessarily, smaller than the total area of tray 180.In some embodiments of the present invention the working area isannular. The working area is shown at 26. In some embodiments of thepresent invention tray 180 rotates continuously in the same directionthroughout the formation of object, and in some embodiments of thepresent invention tray reverses the direction of rotation at least once(e.g., in an oscillatory manner) during the formation of the object.Tray 180 is optionally and preferably removable. Removing tray 180 canbe for maintenance of system 101, or, if desired, for replacing the traybefore printing a new object. In some embodiments of the presentinvention system 101 is provided with one or more different replacementtrays (e.g., a kit of replacement trays), wherein two or more trays aredesignated for different types of objects (e.g., different weights)different operation modes (e.g., different rotation speeds), etc. Thereplacement of tray 180 can be manual or automatic, as desired. Whenautomatic replacement is employed, system 101 comprises a trayreplacement device 36 configured for removing tray 180 from its positionbelow heads 116 and replacing it by a replacement tray (not shown). Inthe representative illustration of FIG. 2A tray replacement device 36 isillustrated as a drive 38 with a movable arm 40 configured to pull tray180, but other types of tray replacement devices are also contemplated.

Exemplified embodiments for the printing head 116 are illustrated inFIGS. 3A-3C. These embodiments can be employed for any of the AM systemsdescribed above, including without limitation, system 100 and system101.

FIGS. 3A-B illustrate a printing head 116 with one (FIG. 3A) and two(FIG. 3B) nozzle arrays 122. The nozzles in the array are preferablyaligned linearly, along a straight line. In embodiments in which aparticular printing head has two or more linear nozzle arrays, thenozzle arrays are optionally and preferably can be parallel to eachother.

When a system similar to system 100 is employed, all printing heads 116are optionally and preferably oriented along the indexing direction withtheir positions along the scanning direction being offset to oneanother.

When a system similar to system 101 is employed, all printing heads 116are optionally and preferably oriented radially (parallel to the radialdirection) with their azimuthal positions being offset to one another.Thus, in these embodiments, the nozzle arrays of different printingheads are not parallel to each other but are rather at an angle to eachother, which angle being approximately equal to the azimuthal offsetbetween the respective heads. For example, one head can be orientedradially and positioned at azimuthal position φ₁, and another head canbe oriented radially and positioned at azimuthal position φ2. In thisexample, the azimuthal offset between the two heads is φ₁-φ₂, and theangle between the linear nozzle arrays of the two heads is also φ₁-φ₂.

In some embodiments, two or more printing heads can be assembled to ablock of printing heads, in which case the printing heads of the blockare typically parallel to each other. A block including several inkjetprinting heads 116 a, 116 b, 116 c is illustrated in FIG. 3C. In someembodiments, system 101 comprises a stabilizing structure 30 positionedbelow heads 116 such that tray 180 is between support structure 30 andheads 116. Stabilizing structure 30 may serve for preventing or reducingvibrations of tray 180 that may occur while inkjet printing heads 116operate. In configurations in which printing heads 116 rotate about axis14, stabilizing structure 30 preferably also rotates such thatstabilizing structure 30 is always directly below heads 116 (with tray180 between heads 116 and tray 180).

Tray 180 and/or printing heads 116 is optionally and preferablyconfigured to move along the vertical direction z, parallel to verticalaxis 14 so as to vary the vertical distance between tray 180 andprinting heads 116. In configurations in which the vertical distance isvaried by moving tray 180 along the vertical direction, stabilizingstructure 30 preferably also moves vertically together with tray 180. Inconfigurations in which the vertical distance is varied by heads 116along the vertical direction, while maintaining the vertical position oftray 180 fixed, stabilizing structure 30 is also maintained at a fixedvertical position.

The vertical motion can be established by a vertical drive 28. Once alayer is completed, the vertical distance between tray 180 and heads 116can be increased (e.g., tray 180 is lowered relative to heads 116) by apredetermined vertical step, according to the desired thickness of thelayer subsequently to be printed. The procedure is repeated to form athree-dimensional object in a layer-wise manner.

In some embodiments of the invention, system 101 further comprises oneor more leveling devices 32 which can be manufactured as a roller or ablade. Leveling device 32 serves to straighten the newly formed layerprior to the formation of the successive layer thereon. In someembodiments, leveling device 32 has the shape of a conical rollerpositioned such that its symmetry axis 34 is tilted relative to thesurface of tray 180 and its surface is parallel to the surface of thetray. This embodiment is illustrated in the side view of system 101(FIG. 2B).

The conical roller can have the shape of a cone or a conical frustum.

The opening angle of the conical roller is preferably selected such thatis a constant ratio between the radius of the cone at any location alongits axis 34 and the distance between that location and axis 14. Thisembodiment allows roller 32 to efficiently level the layers, since whilethe roller rotates, any point p on the surface of the roller has alinear velocity which is proportional (e.g., the same) to the linearvelocity of the tray at a point vertically beneath point p. In someembodiments, the roller has a shape of a conical frustum having a heighth, a radius R₁ at its closest distance from axis 14, and a radius R₂ atits farthest distance from axis 14, wherein the parameters h, R₁ and R₂satisfy the relation R₁/R₂=(R−h)/h and wherein R is the farthestdistance of the roller from axis 14 (for example, R can be the radius oftray 180).

In some embodiments of the present invention printing heads 116 areconfigured to reciprocally move relative to tray along the radialdirection r. These embodiments are useful when the lengths of the nozzlearrays 122 of heads 116 are shorter than the width along the radialdirection of the working area 26 on tray 180. The motion of heads 116along the radial direction is optionally and preferably controlled bycontroller 152.

Any of systems 100 and 101 may optionally and preferably comprise asolidifying device 124 which can include any device configured to emitlight, heat or the like that may cause the deposited materialformulation to harden. For example, solidifying device 124 can compriseone or more radiation sources, which can be, for example, an ultravioletor visible or infrared lamp, or other sources of electromagneticradiation, or electron beam source, depending on the building materialformulation being used. The radiation source can include any type ofradiation emitting device, including, without limitation, light emittingdiode (LED), digital light processing (DLP) system, resistive lamp andthe like. In some embodiments of the present invention, solidifyingdevice 124 serves for curing or solidifying the building materialformulation, e.g. the model material and the support material.

In any of systems 100 and 101, the operation of the inkjet printingheads and optionally and preferably also of one or more other componentsof the system, e.g., the motion of the tray, the operation of the supplysystem, the activation, deactivation, applied voltage, and positionalong the vertical and/or horizontal direction of the leveling deviceand/or the solidifying device, etc. are controlled by a controller 152.The controller can have an electronic circuit and a non-volatile memorymedium readable by the circuit, wherein the memory medium stores programinstructions which, when read by the circuit, cause the circuit toperform control operations as further detailed below.

The controller preferably communicates with a data processor or hostcomputer 154 which transmits digital data pertaining to fabricationinstructions based on computer object data, e.g., a Computer-AidedDesign (CAD) configuration represented on a computer readable medium ina form of a Standard Tessellation Language (STL) or a StereoLithographyContour (SLC) format, Virtual Reality Modeling Language (VRML), AdditiveManufacturing File (AMF) format, Drawing Exchange Format (DXF), PolygonFile Format (PLY) or any other format suitable for CAD. Typically, thecontroller controls the voltage applied to each dispensing head ornozzle array and the temperature of the building material formulation inthe respective printing head. Generally, controller 152 controlsprinting heads to dispense, droplets of building material formulation inlayers, such as to print a three-dimensional object. In system 101,controller 152 optionally and preferably controls the printing heads todispense the droplets while the tray is rotating.

In some embodiments, the controller receives additional input from theoperator, e.g., using data processor 154 or using a user interface 116communicating with the controller. User interface 116 can be of any typeknown in the art, such as, but not limited to, a keyboard, a touchscreen and the like. For example, controller 152 can receive, asadditional input, one or more building material formulation types and/orattributes, such as, but not limited to, color, characteristicdistortion and/or transition temperature, viscosity, electricalproperty, magnetic property. Other attributes and groups of attributesare also contemplated.

The object data formats are typically structured according to aCartesian system of coordinates. In these cases, when system 101 isemployed, computer 154 preferably executes a procedure for transformingthe coordinates of each slice in the computer object data from aCartesian system of coordinates into a polar system of coordinates.Computer 154 optionally and preferably transmits the fabricationinstructions in terms of the transformed system of coordinates.Alternatively, computer 154 can transmit the fabrication instructions interms of the original system of coordinates as provided by the computerobject data, in which case the transformation of coordinates is executedby the circuit of controller 152.

The transformation of coordinates allows three-dimensional printing overa rotating tray. In system 101, not all the nozzles of the head pointscover the same distance over tray 180 during at the same time. Thetransformation of coordinates is optionally and preferably executed soas to ensure equal amounts of excess building material formulation atdifferent radial positions. Representative examples of coordinatetransformations according to some embodiments of the present inventionare provided in FIGS. 4A-B, showing three slices of an object (eachslice corresponds to fabrication instructions of a different layer ofthe objects), where FIG. 4A illustrates a slice in a Cartesian system ofcoordinates and FIG. 4B illustrates the same slice following anapplication of a transformation of coordinates procedure to therespective slice.

Some embodiments contemplate the fabrication of an object by dispensingdifferent building material formulations from different dispensingheads. These embodiments provide, inter alia, the ability to selectmaterial formulations from a given number of building materialformulations and define desired combinations of the selected materialformulations and their properties. According to the present embodiments,the spatial locations of the deposition of each material formulationwith the layer is defined, either to effect occupation of differentthree-dimensional spatial locations by different building materialformulations, or to effect occupation of substantially the samethree-dimensional location or adjacent three-dimensional locations bytwo or more different building material formulations so as to allow postdeposition spatial combination of the building material formulationswithin the layer, thereby to form a composite material formulation atthe respective location or locations.

Any post deposition combination or mix of modeling material formulationsis contemplated. For example, once a certain material formulation isdispensed it may preserve its original properties. However, when it isdispensed simultaneously with another modeling material formulation orother dispensed material formulations which are dispensed at the same ornearby locations, a composite material formulation having a differentproperty or properties to the dispensed material formulations is formed.

The present embodiments thus enable the deposition of a broad range ofmaterial formulation combinations, and the fabrication of an objectwhich may consist of multiple different combinations of materialformulations, in different parts of the object, according to theproperties desired to characterize each part of the object.

Further details on the principles and operations of an AM systemsuitable for the present embodiments are found in U.S. PublishedApplication Nos. 20100191360 and 20170173886, the contents of which arehereby incorporated by reference.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings. The invention is capable of otherembodiments or of being practiced or carried out in various ways.

Reference is now made to FIGS. 5A and 5B showing simplified schematicdrawings of a cross sectional view of an object fabricated with a corefilled with a non-reactive formulation encompassed by a shell formedwith a reactive formulation, and a top view of a single layer of theobject respectively, both in accordance with some example embodiments.According to some example embodiments, an object 112 may include a core210 that is formed with a second building (e.g., modeling) materialformulation or a non-reactive formulation configured to be partiallycured during the AM process and a shell 220 formed with a first building(e.g., modeling) material formulation or a reactive formulation that isconfigured to be fully cured during the AM process. Optionally, one ormore support structures 115 may be formed to support object 112. Thesupport structure may be solidified by curing during the AM process.According to some example embodiments, core 210 is maintained in asemi-solidified state, e.g. liquid-jelly state during the AM processwhile shell 220 is solidified during the AM process.

Referring now to FIG. 5B, according to some example embodiments, duringthe AM process, a layer 113 may be printed with an outer region 221formed with the first building (e.g., modeling) material formulationthat may define a perimeter of layer 113 and an inner region 211 formedwith the second building (e.g., modeling) material formulation that isat least partially encompassed by outer region 221. According to someexample embodiments, a plurality of layers that form object 112 areformed in a manner similar to layer 113 including both outer region 221and inner region 211. The plurality of layers may optionally form shell220 and core 210. Shell 220 may be defined to encapsulate core 210. Inother example embodiments, object 112 may not be fully encapsulated byshell 220. A thickness of outer region 221 may be defined to have athickness of one printed voxel or a thickness of 0.1-2 mm, e.g. 0.3-1 mmor 0.3 mm.

Optionally, the first building (e.g., modeling) material formulationapplied to form outer region 221 is reactive and includes aphoto-initiator. As such the first building material formulationsolidifies based on a curing process, e.g. UV radiation radiated duringthe AM process. In some example embodiments, inner region 211 formedwith the second building (e.g., modeling) material formulation mayinclude relatively low concentration or no photo-initiator and may notsolidify or may not fully solidify with the radiation, e.g. the UVradiation radiated during the AM process. Rather, core 210 formed with aplurality of inner regions 211 may be solidified in a post treatmentprocess, e.g. thermal curing process. In some example embodiments aconcentration of photo-initiator in the formulation of inner region 211may be between 0.02 wt. %-0.1 wt. while the concentration ofphoto-initiator in the formulation of outer region 221 may be between 2wt. %-5 wt. %.

In some example embodiments, the second building (e.g., modeling)material formulation used to form inner region 211 is prone to shrinkingwhen cured. Second building (e.g., modeling) material formulation whenhardened may for example have a Tg and/or HDT above a printingtemperature of steady state temperature of object 112 during printing,e.g. 50° C.-90° C. or above 70° C.

FIGS. 6A and 6B show simplified schematic drawings of a cross sectionalview of an object fabricated with a core filled with non-reactiveformulation (e.g., a sub-formulation of a second formulation asdescribed herein, or a second formulation as described herein), ditheredwith a reactive formulation (e.g., another sub-formulation of a secondformulation as described herein, or a first formulation as describedherein, respectively) and encompassed by another reactive formulation (afirst formulation as described herein) and a top view of a single layerof the object respectively, both in accordance with some exampleembodiments. In some example embodiments, a degree at which core 210 issolidified may be controlled by selectively dithering inner region 211with drops 215 of the first building material formulation or otherreactive formulation (e.g., a sub-formulation of the second formulationas described herein). In some example embodiments, a concentration ofdithering is adapted to geometry of object 112 or layer 113 so that someportions of object 112 or layer 113 may be solidified to a higher degreethan other portions.

FIG. 7 is a simplified schematic drawing of a cross-sectional view of anobject encapsulated in support material in accordance with some exampleembodiments. According to some example embodiments, support material 115is applied to form a shell 218 that encapsulates object 112 formed witha non-reactive formulation. Shell 218 formed with support material isexternal to object 112 and may be sacrificial, e.g. removed after posttreating object 112 with support material 115. Support material 115 maybe fully cured during the AM process.

FIG. 8 is a simplified flow chart of an example method to fabricate anobject with reduced asymmetrical shrinking in accordance with someexample embodiments. According to some example embodiments, a dataprocessor associated with an inkjet printing system is configured toreceive object data and define geometry of a shell around the object(block 310). Defining geometry of the shell may include defining athickness of the shell. Optionally the thickness may be selectivelydefined to vary based on the geometry of the object. The shell may bepart of a volume of the object or may be external to the object andconfigured to be removed at the end of the AM process. In some exampleembodiments, a degree of desired solidification in the core may also bedefined (block 320). The core may be formed by non-reactive formulation(a second formulation as described herein) or a combination of reactiveand non-reactive formulation (e.g., either a first and secondformulations as described herein, or sub-formulations of the secondformulation as described herein). The degree of solidification of thecore may be selectively defined based on adding a vol. % of the reactiveformation in the core.

In some example embodiments, the model of the object including thedefined shell and core is divided into printable layers (block 330).During printing, the printer selectively deposits the reactiveformulation, the non-reactive formulation and support material per layer(block 340). Optionally, the layer is leveled (block 350) and then cured(block 360). This process may continue until all the layers are built(block 370). At the end of the layer building process, exposure to asecond curing condition (e.g., thermal post treatment) (block 380) maybe performed to complete solidification of the object, e.g. the core.Thermal post treatment may include for example heating the object for1-10 hours at a temperature of 100° C. to 250° C., or 150° C. to 250° C.Thermal post treatment can be performed gradually, by heating to a firsttemperature in the above-indicated range for a first time period (e.g.,1-4 hours) and then to a second temperature, higher than the firsttemperature for a second time period (e.g., 1-4 hours) and optionally toa third, fourth, etc. temperature, for additional time periods. Thesupport material when present may be removed before or after theexposure to the second curing condition (block 390). Alternatively, thesecond curing condition may be exposing the object to room temperature,e.g. 15° C.-30° C. for a defined period, e.g., 1-48 hours.

FIG. 9 is a simplified block diagram of an example ink-jet printingsystem for three dimensional printing in accordance with some exampleembodiments. According to some example embodiments, an ink-jet printingsystem 200 may be similar to inkjet system 100 but with a plurality ofadaptions to configure the system for printing with materials accordingto the present embodiments (e.g., materials that have a relatively highHDT or that otherwise tend to shrink due solidification withsolidification system 124, materials that form transparent objects, andany other materials and/or methods for which the present embodiments arebeneficial, as described herein). According to some example embodiments,preferably a building material supply system or apparatus 130′ containsat least one container or cartridge with building (e.g., modeling)material formulation that is of a non-reactive formulation (a secondformulation as described herein) and another container or cartridge withbuilding (e.g., modeling) material that is of a reactive formulation (afirst formulation as described herein). According to some exampleembodiments, a data processor 154′ is configured to obtain computerobject data and to compute digital data defining a shell and a core ofobject 112. A thickness of the shell may be defined with data processor154′ based on the shape of object 112, the size of object 112 andmaterial selected to fabricate object 112. In some example embodiments,parameters for dithering a reactive formulation as described herein inthe core is also defined by data processor 154′ also based on the shapeof object 112, the size of object 112 and material selected to fabricateobject 112. Parameters for dithering include vol. % of material ditheredand may also include pattern for dithering. Optionally, the vol. % ofmaterial dithered may be different for different layers and may beadapted to the shape of object 112. Optionally, the pattern of materialdithered may be different for different layers. In some exampleembodiments, data processor 154′ may also be configured to define a meshstructure or an array of pillars within the core of object 112 that isformed from a reactive formulation. According to some exampleembodiments, ink-jet printing system 200 additionally includes a heatingchamber 190 configured for receiving object 112 printed with inkjetprinter 114 and post treating the object at the end of the AM process.

FIG. 10 is an example pixel map for a curling bar model to be printedbased on some example embodiments. In the pixel map shown, the coreincludes 92 vol. % of a non-reactive formulation (shown in red), e.g., asub-formulation of a second formulation as described herein, that isdithered with 8 vol. % of a reactive formulation (shown blue), e.g.,another sub-formulation of a second formulation as described herein. Insome example embodiments, the non-reactive formulation may be a modifiedformulation of TangoBlack™ and the reactive formulation may beVeroWhite™, both available by Stratasys® Ltd., Israel. The shell (shownin green) may be formed from a formulation that provides, when hardened,a relatively high HDT material. In the example shown, the shell isformed from RGD515™ as an example first formulation, also available byStratasys® Ltd, Israel. Optionally, RGD515™ provides improved impactresistance. Exemplary configurations and modeling material formulations:

The additive manufacturing of the present embodiments employs aformulation system that comprises a first building (e.g., modeling)material formulation (herein also referred to as a first formulation),which is reactive towards a first curing condition and a second building(e.g., modeling) material formulation (herein also referred to as asecond formulation), which is non-reactive or partially reactive towardsa first curing condition, and is effected while controlling the curingparameters such that upon exposure to a first curing condition the firstformulation hardens while the second formulation remains uncured orpartially hardened, according to the configurations describedhereinabove.

In some of any of the embodiments described herein, each of the firstand second building material formulations is a modeling materialformulation, which forms the final object.

According to some embodiments of the present invention, in at least aportion of the dispensed layers, the first and second formulations aredispensed as described herein, and exposed to a first curing condition.The first and the second building material formulations and the firstcuring condition are selected such that upon exposure to the firstcuring condition, the first building material formulation is hardened toa higher degree than the second building formulation. The first and thesecond building material formulations and the first curing condition areselected such that upon exposure to the first curing condition, thefirst building material formulation provides a hardened material havinga high hardening degree, whereby the second building materialformulation does not undergo hardening or provides a material with ahardening degree that is lower than that provided by the firstformulation.

According to some embodiments of the present invention, the first andthe second building material formulations and the first curing conditionare selected such that upon exposure to the first curing condition, ahardening kinetic parameter of the first formulation is higher than thatof the second formulation. In some embodiments, the hardening kineticparameter is a rheological kinetic parameter such as a rate of a changein the viscosity of the formulation, and/or a rate of a change in thetan δ of the formulation. These kinetic parameters can be measured bymethods known to those skilled in the art.

In some embodiments, a hardening kinetic parameter of the firstformulation is higher than that of the second formulation by at least2-folds, or at least 5-folds, or at least 10-folds. A rate in the changeof viscosity can be measured by measuring the viscosity of a formulationat a constant temperature and when exposed to the first curing conditionat different time points. Viscosity can be measured, for example, on aBrookfield viscometer.

By “Tan δ”, which is also known and used in the art as “tan delta”,“tangent delta”, “loss tangent”, it is meant a ratio of loss modulus tostorage modulus, or the tangent of the phase lag between the stress andthe strain.

In some of any of the embodiments described herein, upon exposure to thefirst curing condition, the first formulation provides a material thatfeatures a hardening degree, as defined herein, that is higher by atleast 50%, or at least 60%, or at least 70%, or at least 80%, or atleast 90%, or more, than a hardening degree of a material that is formedupon exposing the second formulation to the first curing condition.

In some of any of the embodiments described herein, the firstformulation is such that provides, upon exposure to the first curingcondition, a hardening degree, as defined herein, of at least 50%, or atleast 60%, preferably at least 70%, or at least 80%, or at least 90%, oreven 100%. For example, in some embodiments, the first formulationcomprises one or more curable materials which are polymerizablematerials, and the hardening degree represents the mol % of the curablematerials that polymerize upon exposure to the curing condition, suchthat at least 50 mol %, or at least 60 mol %, preferably at least 70 mol%, or at least 80 mol %, or at least 90 mol %, or all of thepolymerizable materials, undergo polymerization to thereby provide ahardened first formulation. Since the first formulation undergoes a highdegree of hardening when exposed to the first curing condition, it isreferred to herein as a reactive formulation, that is, the firstformulation is reactive towards hardening when exposed to the firstcuring condition.

In some of any of the embodiments described herein, the secondformulation is such that provides, upon exposure to the first curingcondition, a hardening degree, as defined herein, of no more than 50%,or no more than 40%, preferably no more than 30%, or no more than 20%,or no more than 10%, or no more than 5%, or even null. For example, insome embodiments, the second formulation comprises one or more curablematerials which are polymerizable materials, and the hardening degreerepresents the mol % of the curable materials that polymerize uponexposure to the curing condition, such that at no more 50 mol %, or nomore than 40 mol %, preferably no more than 30 mol %, or no more than 20mol %, or no more than 10 mol %, or no more than 5 mol %, or none, ofthe polymerizable materials, undergo polymerization. Since the secondformulation undergoes a low or null degree of hardening when exposed tothe first curing condition, it is referred to herein as a non-reactiveor partially-reactive formulation, that is, the second formulation isnon-reactive or partially-reactive towards hardening when exposed to thefirst curing condition.

A hardening degree as defined herein can be determined or measured, forexample, by determining a hardening parameter of the first and secondformulations when exposed to the first curing condition.

The hardening parameter can be, for example, a rheological parametersuch as the viscosity of the formulation upon exposure to the firstcuring condition, and/or the loss tangent (tan δ) of the formulationupon exposure to the first curing condition.

According to some embodiments of the present invention, the first andthe second building material formulations and the first curing conditionare selected such that upon exposure to the first curing condition, achange in a hardening parameter of the first formulation is higher thana change in a hardening parameter of the second formulation.

By “a change in a hardening parameter” in the context of “upon exposureto the first curing condition” it is meant a change in a hardeningparameter, as described herein, during the time T, wherein T representsthat time period from when the first curing condition is applied to adispensed layer and until the following layer is dispensed.

According to some embodiments of the present invention, the first andthe second building material formulations and the first curing conditionare selected such that upon exposure to the first curing condition, achange in a viscosity of the first formulation is higher than a changein a viscosity of the second formulation.

According to some of these embodiments, a change in the viscosity of thefirst formulation is higher than that of the second formulation by atleast 2-folds, or at least 5-folds, or at least 10-folds.

According to some of these embodiments, a change in the viscosity of thefirst formulation during the time T as defined herein is at least2-folds, such that the viscosity of the first formulation increases byat least 2-folds or by at least 5-folds or by at least 10-folds.According to some of these embodiments, a change in the viscosity of thesecond formulation during the time T as defined herein is null, that is1-folds, or is lower than 2-folds, and can be, for example, 1.1, 1.2,1.3, 1.4 or 1.5-folds.

According to some embodiments of the present invention, the first andthe second building material formulations and the first curing conditionare selected such that upon exposure to the first curing condition, achange in a loss tangent of the first formulation is higher than achange in a loss tangent of the second formulation.

According to some of these embodiments, a change in the loss tangent ofthe first formulation is higher than that of the second formulation byat least 2-folds, or at least 5-folds, or at least 10-folds.

According to some of these embodiments, a change in the loss tangent ofthe first formulation during the time T as defined herein is of at leastone unit, such that the loss tangent of the first formulation increasesby at least one unit, or at least 2 units, or more. According to some ofthese embodiments, a change in the loss tangent of the secondformulation during the time T as defined herein is null, or is lowerthan one unit, or lower than 0.5 units, and can be, for example, 0.1,0.2, 0.3, 0.4 or 0.5 units.

In some of any of the embodiments described herein, the first and secondformulations are curable formulations, each of which can form a hardenedmaterial when exposed to a suitable curing condition.

In some of any of the embodiments described herein, the firstformulation hardens when exposed to the first curing condition, and thesecond formulation does not harden, or hardens to a lesser degree, asdescribed herein, when exposed to the first condition and hardens orhardens further when exposed to a second curing condition that isdifferent from the first curing condition. It is to be noted that insome embodiments, the first formulation can further harden when exposedto the second curing condition.

In some of any of the embodiments described herein, the first curingcondition is optical radiation, as described herein, for example, a UVradiation, and the second curing condition is heat, as described herein.Alternatively, both the first and second curing conditions are opticalradiation, and the first and second curing conditions differ in the typeand/or wavelength of the optical radiation. Further alternatively, boththe first and second curing conditions are heat, and the first andsecond curing conditions differ in the applied temperature. Furtheralternatively, the first curing condition is heat, as described hereinand the second curing condition is optical radiation, as describedherein, for example, a UV radiation.

In some of the embodiments where the first curing condition comprisesoptical radiation and the second curing condition comprises heat, thetemperature at which the first curing condition is applied is lower byat least 50° C. or at least 100° C. from the temperature applied in thesecond curing condition

In some of the embodiments where the first curing condition comprisesheat and the second curing condition comprises optical radiation, thefirst curing condition is devoid of optical radiation, that is, nooptical radiation is applied, and if the second curing conditioncomprises visible light, respective masking is affected.

In some of any of the embodiments described herein, the firstformulation comprises one or more curable materials which arecollectively referred to herein as a first curable material.

In some of any of the embodiments described herein, the secondformulation comprises one or more curable materials which arecollectively referred to herein as a second curable material.

In some of any of the embodiments described herein, the first curablematerial undergoes polymerization when exposed to the first curingcondition, and the second formulation does not undergo polymerization ordoes not undergo complete polymerization, or undergoes polymerization toa degree that is lower than a polymerization degree of the firstformulation, when exposed to the first condition and undergoespolymerization to a higher degree (e.g., complete polymerization) whenexposed to the second curing condition that is different from the firstcuring condition. It is to be noted that in some embodiments, the firstcurable material undergoes further polymerization (to a higher degree)and/or cross-linking also when exposed to the second curing condition.

Each of the first and second formulations can further comprise,independently, one or more agents that promote the hardening of at leastsome of the curable materials, collectively referred to herein as aninitiator. In some embodiments, the initiator initiates thepolymerization and/or cross-linking of curable (e.g., polymerizableand/or cross-linkable) materials.

In the context of AM in general and the AM of the present embodiments,an initiator is a chemical material that initiates and/or facilitates(increases the rate of, and/or reduces the energy required for) thepolymerization and/or cross-linking of polymerizable materials.Typically, the initiator generates a reactive species that initiatesand/or facilitates (increases the rate of, and/or reduces the energyrequired for) the reaction. For example, initiators of free-radicalpolymerization generate a free radical, and the presence of the freeradical initiates and/or facilitates the free-radical polymerization.Similarly, initiators of cationic polymerization generate a cation;initiators of anionic polymerization generate an anion; and otherinitiators form other species that initiate or facilitatepolymerization.

The initiator can be active towards the polymerization when contacting arespective curable material, or, can be chemically inactive towardshardening of curable materials, for example, it does not initiate orfacilitate the polymerization and/or cross-linking of polymerizablematerials, without being exposed to a curing condition. The curingcondition activates the initiator, typically such that it generates thereactive species which initiates and/or facilitates polymerization ofrespective polymerizable materials at its vicinity.

Initiators that are activated by irradiation are photoinitiators.Initiators that are activated by heat are thermal initiators. Initiatorscan alternatively be chemically activated by contacting another chemicalagent, which is also known as an activator. Further alternatively,initiators can be activated by a curing condition, and generate areactive species by contacting an activator.

The activity of an initiator (optionally in combination with anactivator) towards hardening of formulations that comprise curablematerials (e.g., towards polymerization and/or cross-linking) depends onthe exposure to a condition that generates the reactive species, and/oron the relative amount or concentration of the initiator and the curablematerials. When the concentration of an initiator is too low, itsactivity is low due to (i) small amount of the generated reactivespecies, which can be even smaller since the bulk of curable materialsmay mask the curing condition and reduce the amount of reactive speciesto be generated; and/or (ii) generation of low concentration of thereactive species in the bulk of curable materials results in loweramount of molecules of the respective curable material (or activator)that contact the reactive species for initiation and/or facilitation ofthe polymerization process.

In some of any of the embodiments described herein, an initiator isactive towards polymerization of polymerizable materials (and therebytowards hardening of a formulation or formulation system comprisingsame) when it is capable to generate, preferably upon exposure to asuitable curing condition, reactive species at a concentrationsufficient to induce polymerization of at least 50%, or at least 60%, orat least 70% of the polymerizable materials.

In some of any of the embodiments described herein, an initiator isinactive towards polymerization of polymerizable materials (and therebytowards hardening of a formulation comprising same) when it is incapableto generate, preferably upon exposure to a suitable curing condition,reactive species at a concentration sufficient to induce polymerizationof at least 50%, or at least 60%, or at least 70% of the respectivepolymerizable materials.

In some of any of the embodiments described herein, an initiator isconsidered inactive or partially active towards polymerization ofpolymerizable materials (and thereby towards hardening of a formulationcomprising same) when it generates, preferably upon exposure to a curingcondition, reactive species at a concentration that inducespolymerization of no more than 50%, or no more than 40%, or no more than30%, preferably no more than 20%, or no more than 10%, or no more than5%, or none, of the respective polymerizable materials.

The initiator can be inactive towards the polymerization when it is notexposed to a curing condition that generates a sufficient amount ofreactive species and/or when it is present in a low concentration asdescribed herein.

In some embodiments, the initiator is inactive when it is in an amountthat is less than 50%, or less than 30%, or less than 10% by weight, orless than 5%, or less than 1% of an amount of the initiator required forpromoting hardening of at least 70% of the second curable material uponexposure to the first curing condition.

The absolute amount of an initiator that is required for promotinghardening of at least 70% of the second curable material upon exposureto the first curing condition depends, at least in part, on the type ofthe second curable material and its consequent reactivity.

Typically, but not limiting, an initiator is active towardspolymerization, as defined herein, when it is present at a concentrationof from 0.5 to 5 weight percent relative to the total weight of therespective curable material(s), preferably at a concentration of fromabout 1 to about 3 weight percents, e.g., of 2.5 weight percent, andwhen it is exposed to a suitable curing condition.

Typically, but not limiting, an initiator is inactive or is partiallyactive towards polymerization, as defined herein, when it is present ata concentration lower than 0.1, or lower than 0.05, e.g., of 0.025,weight percent relative to the weight of the respective curablematerial(s), even when it is exposed to a suitable curing condition.

In some of any of the embodiments described herein, an initiator isinactive towards hardening of the second formulation by being incapableof generating a sufficient amount of reactive species when exposed tothe first curing condition.

In some of these embodiments, the initiator is in an amount sufficientto promote hardening of the second formulation when exposed to a curingcondition other than the first curing condition. Alternatively, theinitiator is in an amount that is insufficient to promote hardening ofthe second formulation even when exposed to a curing condition otherthan the first curing condition.

In some of any of the embodiments described herein, the firstformulation is a photocurable formulation (e.g., UV-curable formulation)which comprises a photocurable material (e.g., UV-curable materialand/or a photoinitiator for promoting the hardening) and the secondcurable formulation is a thermally curable formulation, which comprisesa thermally-curable material and/or an agent that promotes hardeningwhen exposed to heat). Alternatively, both the first and secondformulations are UV-curable. Further alternatively, both the first andsecond formulations are thermally curable. Further alternatively, thefirst formulation is thermally curable and the second formulation is aphotocurable formulation (e.g., UV-curable formulation).

In some of any of the embodiments described herein, the firstformulation comprises a first curable material and one of the first andsecond formulations comprises an initiator that is active towardshardening of the first formulation, preferably upon exposure to a firstcuring condition.

In some of these embodiments, the initiator is included in the firstformulation, and promotes the hardening of the first formulation once itis exposed to the first curing condition.

In some of these embodiments, the initiator is included in the secondformulation and promotes the hardening of the first formulation when thefirst and second formulations are dispensed and contact one another, andpreferably, are also exposed to the first curing condition. In some ofthese embodiments, the dispensing is such that the amount of theinitiator in the second formulation and the ratio of the first andsecond formulations at a desired location are such that the initiator isactive towards hardening of the first formulation, as defined herein,e.g., the initiator can generate, upon exposure to the first curingcondition, a sufficient amount of reactive species relative to theamount of the first curable material, at the desired location, such thata degree of hardening of the first formulation at the desired locationis as defined herein (e.g., at least 70%). Such embodiments aredesirable when the curable materials are highly reactive such thathardening can occur even at the presence of minute amounts of reactivespecies, and hence it is desirable to separate the initiator from therespective first curable material before and during the dispensing ofthe formulations.

In some of any of the embodiments described herein, the secondformulation comprises a second curable material and one of the first andsecond formulations comprises an initiator that is inactive or ispartially active towards the hardening of the second formulation uponexposure to the first curing condition.

In some of these embodiments, the initiator is included in the secondformulation, and is inactive towards promoting the hardening of thesecond formulation (e.g., does not generate a reactive species in asufficient amount for initiating or facilitating polymerization of thesecond curable material) when it is exposed to the first curingcondition.

In some embodiments, corresponding to the configuration shown in FIGS.6A and 6B, the second material formulation forming the inner regioncomprises two sub-formulations referred to herein as sub-formulation Aand B, each comprising the same second curable material (or a mixture oftwo or more second curable materials), whereby sub-formulation A hardensto a higher degree than sub-formulation B when exposed to the firstcuring condition.

In some of these embodiments, sub-formulation A comprises a secondcurable material and an initiator for promoting polymerization of thesecond curable material, as described herein, and the initiator isactive towards promoting the polymerization of the second curablematerial when exposed to the first curing condition, as described hereinin any of the respective embodiments and any combination thereof. Inthese embodiments, sub-formulation B comprises the second curablematerial and is either devoid of an initiator or comprises an initiatorthat is inactive towards polymerization of the second curable materialwhen exposed to the curing condition, as described herein in any of therespective embodiments and any combination thereof. In some of theseembodiments, sub-formulation B comprises an initiator that is activetowards the polymerization of the second material but is in amount thatgenerates, upon exposure to a curing condition, reactive species at aconcentration that induces polymerization of no more than 50%, or nomore than 40%, or no more than 30%, preferably no more than 20%, or nomore than 10%, or no more than 5%, or none, of the second curablematerial.

In some of these embodiments, each of sub-formulations A and B comprisesthe same curable material and the same initiator, and the initiator isactive when exposed to the first curing condition. In these embodiments,an amount of the initiator in sub-formulation A is higher by at least100% of an amount of the initiator in sub-formulation B, and can behigher by 2-folds, 3-folds, 4-folds, and even more relative to theamount of the initiator in sun-formulation B. In some of theseembodiments, a weight ratio of sub-formulations A and B is lower than0.5, that is, a total amount of sub-formulation A in the inner region isno more than 50% by weight of the total amount of sub-formulation B inthe inner region, and is preferably no more than 40%, or no more than30%, or no more than 20%, or no more than 10%, or no more than 5%, or nomore than 1%, and even less, by weight, of the total amount ofsub-formulation B in the inner region.

The following describes exemplary formulation systems that are usable inthe additive manufacturing of the present embodiments.

A first exemplary formulation system, also referred to herein asformulation system I, comprises a first formulation which comprises afirst curable material (or a mixture of one or more first curablematerials); and a second formulation which comprises a second curablematerial (or a mixture of one or more second curable materials), and thesecond curable material is different from the first curable material.

In some embodiments of exemplary formulation system I, the firstformulation undergoes hardening of at least 70% when exposed to thefirst curing condition and the second formulation undergoes hardening ofno more than 30% when exposed to the first curing condition.

In some embodiments of exemplary formulation system I, referred toherein as formulation system Ia, the first formulation further comprisesa first initiator that is active towards hardening the first formulationwhen exposed to the first curing condition and the second formulationcomprises a second initiator that is inactive towards hardening thesecond formulation when exposed to the first curing condition. Thesecond initiator is different from the first initiator.

In exemplary embodiments of formulation system Ia, the first curingcondition is irradiation (e.g., UV-irradiation) and the firstformulation comprises a first curable material that is a photocurablematerial (e.g., UV-curable material) and a photoinitiator suitable forpromoting hardening of the first formulation when exposed to theirradiation, in an amount the induces hardening of at least 70% of thefirst curable material. The second formulation comprises a secondcurable material and an initiator that is inactive, as described herein,when exposed to irradiation. In some embodiments, the initiator is athermal initiator and the curable material is a thermally-curablematerial. In these embodiments, the second curing condition comprisesapplication of heat energy. In some of these embodiments, the firstcuring condition does not comprise application of heat energy. Forexample, the first curing condition is applied at ambient temperature.In some embodiments, the first curing condition is effected at atemperature that is lower by at least 50° C. than a temperature appliedfor the second curing condition.

In some of the embodiments of exemplary formulation system Ia, thesecond formulation comprises two sub-formulations which comprise twocurable systems: one curable system comprises a photocurable material,which can be the same or different from the first curable material inthe first formulation and a photoinitiator that is active towardspromoting polymerization of the respective curable material and anothercurable system comprises the thermally curable material and athermally-activated agent for promoting polymerization of the thermallycurable material. In some of these embodiments, sub-formulation Acomprises the photocurable material and the agent that promotespolymerization of the second, thermally-curable material, andsub-formulation B comprises the thermally-curable material and thephotoinitiator. The ratio between sub-formulation A and sub-formulationB is such that provides, upon exposure to the first curing condition, ahardening degree of the second formulation of no more than 50% or nomore than 30%, as described herein.

In some embodiments of exemplary formulation system I, referred toherein as formulation system Ib, the first formulation further comprisesa first initiator that is active towards hardening the first formulationwhen exposed to the first curing condition and the second formulationcomprises a second initiator that is inactive towards hardening thesecond formulation when exposed to the first curing condition. Thesecond initiator is the same as the first initiator, at least by beingactivated when exposed to the first curing condition.

In exemplary embodiments of formulation system Ib, the first curingcondition is irradiation (e.g., UV-irradiation) and the firstformulation comprises a first curable material that is a photocurablematerial (e.g., UV-curable material) and a photoinitiator suitable forpromoting hardening of the first formulation when exposed to theirradiation, in an amount the induces hardening of at least 70% of thefirst curable material. The second formulation comprises a secondcurable material that is also a photocurable material (e.g., aUV-curable material) and a second initiator which is also aphotoinitiator and is also activatable by the first curing condition andwhich can be the same as the first initiator or different. The amount ofthe second initiator in the second formulation is such that it isinactive or is partially active towards promoting hardening of thesecond formulation, as described herein. In some of these embodiments,the second curing condition is such that promotes hardening of thesecond formulation in the presence of the low amount of the secondinitiator, and can be, for example, application of heat. In some ofthese embodiments, the first curing condition does not compriseapplication of heat energy. For example, the first curing condition isapplied at ambient temperature. In some embodiments, the first curingcondition is effected at a temperature that is lower by at least 50° C.than a temperature applied for the second curing condition.

In additional exemplary embodiments of formulation system Ib, the firstcuring condition is heat energy at a first temperature and the firstformulation comprises a first curable material that is a thermallycurable material and a thermally-activatable initiator suitable forpromoting hardening of the first formulation when exposed to theirradiation, in an amount the induces hardening of at least 70% of thefirst curable material. The second formulation comprises a secondcurable material that is also a thermally curable material and a secondinitiator which is also a thermally activatable initiator and is alsoactivatable by the first curing condition and which can be the same asthe first initiator or different. The amount of the second initiator inthe second formulation is such that it is inactive or is partiallyactive towards promoting hardening of the second formulation, asdescribed herein. In some of these embodiments, the second curingcondition is such promotes hardening of the second formulation in thepresence of the low amount of the second initiator, and can be, forexample, application of heat at a second temperature which is higherthan the first temperature. In some embodiments, the first curingcondition is effected at a temperature that is lower by at least 50° C.than a temperature applied for the second curing condition.

In some of any of the embodiments of formulation systems Ib, the firstand second curable materials differ in at least one property of thehardened material formed thereby, for example, by HDT, Impact,elasticity, etc.

A second exemplary formulation system, also referred to herein asformulation system II, comprises a first formulation which comprises afirst curable material (or a mixture of one or more first curablematerials); and a second formulation which comprises a second curablematerial (or a mixture of one or more second curable materials), and thefirst and second curable materials are the same.

In some embodiments of exemplary formulation system II, the firstformulation undergoes hardening of at least 70% when exposed to thefirst curing condition and the second formulation undergoes hardening ofno more than 30% when exposed to the first curing condition.

In some embodiments of exemplary formulation system II, the firstformulation further comprises a first initiator that is active towardshardening the first formulation when exposed to the first curingcondition and the second formulation comprises a second initiator thatis inactive towards hardening the second formulation when exposed to thefirst curing condition. The second initiator is the same as the firstinitiator, at least by being activated when exposed to the first curingcondition.

In exemplary embodiments of formulation II, referred to herein asformulation system IIa, the first and second curable materials areUV-curable materials that feature, when hardened, the same or similarproperties, and the first and second initiators are bothphotoinitiators. In some of these embodiments, the first curingcondition is irradiation at a wavelength that activates thephotoinitiator. In these embodiments, the amount of the second initiatorin the second formulation is such that renders it inactive towardshardening of the second formulation when exposed to the first curingcondition, as described herein.

In exemplary embodiments of formulation II, referred to herein asformulation system IIb, the first and second curable materials areUV-curable materials and/or thermally-curable materials, that feature,when hardened, the same or similar properties, and the first and secondinitiators are both thermally-activated initiators. In theseembodiments, the first curing condition comprises heat at a temperaturethat activates the thermally-activated initiator. In these embodiments,the amount of the second initiator in the second formulation is suchthat renders it inactive towards hardening of the second formulationwhen exposed to the first curing condition, as described herein.

A third exemplary formulation system, also referred to herein asformulation system III, comprises a first formulation which comprises afirst curable material (or a mixture of one or more first curablematerials); and a second formulation which comprises a second curablematerial (or a mixture of one or more second curable materials), and thefirst and second curable materials can be the same or different from oneanother.

In some embodiments of exemplary formulation system III, the firstformulation undergoes hardening of at least 70% when exposed to thefirst curing condition and the second formulation undergoes hardening ofno more than 30% when exposed to the first curing condition.

In some embodiments of exemplary formulation system III, the firstformulation further comprises a first initiator that is active towardshardening the first formulation when exposed to the first curingcondition and the second formulation comprises a second initiator thatis inactive towards hardening the second formulation when exposed to thefirst curing condition.

In exemplary embodiments of formulation III, referred to herein asformulation system Ma, the first and second curable materials areUV-curable materials that feature, when hardened, the same or similarproperties, and the first and second initiators are bothphotoinitiators. In some of these embodiments, the first curingcondition is irradiation at a wavelength that activates the firstphotoinitiator but not the second photoinitiator. In some of theseembodiments, the amount of the second initiator in the secondformulation can be such that it is active towards hardening the secondformulation when exposed to radiation at a suitable wavelength but isinactive towards hardening of the second formulation when exposed to thefirst curing condition, as described herein.

In exemplary embodiments of formulation III, referred to herein asformulation system IIIb, the first and second curable materials areUV-curable materials and/or thermally-curable materials, that feature,when hardened, the same or similar properties, and the first and secondinitiators are both thermally-activated initiators. In theseembodiments, the first curing condition comprises heat at a temperaturethat activates only the first initiator. In these embodiments, theamount of the second initiator in the second formulation can be suchthat it is active towards hardening of the second formulation whenexposed to a suitable curing condition that is other than the firstcuring condition but is inactive towards hardening of the secondformulation when exposed to the first curing condition, as describedherein. In some of these embodiments, the second initiator is activatedwhen exposed to a temperature that is higher by at least 50° C. or atleast 100° C. than a temperature at which the first initiator isactivated.

According to the present embodiments, once the above-describedformulations systems are dispensed and exposed to the first curingcondition, the plurality of layers are exposed to a second curingcondition, which is other than the first curing condition and isselected to increase the degree that the inner region is hardened.

In some of any of the embodiments described herein, the first curingcondition is radiation and the second curing condition is heat, and thefirst and second formulations are selected accordingly, for example, inaccordance with exemplary embodiments as described herein.

It is to be noted that whenever a formulation is described as reactivewhen exposed to irradiation, by, for example, comprising a photocurablematerial and/or a photoinitiator, the formulation is to be regarded assuch that hardens when exposed to radiation at low temperatures, forexamples, at a temperature lower than 100° C., or lower than 80° C., orlower than 70° C., or lower than 60° C., or lower than 50° C., or lowerthan 40° C. and even at room temperature. However, such formulations canalso be reactive when exposed to heat, without irradiation at highertemperatures, for example, higher than 100° C., or higher. Thus, suchformulations, which are reactive towards to hardening when exposed to afirst curing condition which is irradiation, can undergo furtherhardening when exposed to a second condition which is heat.

It is to be noted that whenever a formulation is described asnon-reactive or partially-reactive when exposed to irradiation, by, forexample, comprising a photocurable material and/or a photoinitiatorwhich is inactive towards promoting hardening the second formulation,the second formulation is to be regarded such that does not harden, orthat hardens to a low hardening degree as defined herein, when exposedto radiation at low temperatures, for examples, at a temperature lowerthan 100° C., or lower than 80° C., or lower than 70° C., or lower than60° C., or lower than 50° C., or lower than 40° C. and even at roomtemperature. However, such formulations can also be reactive whenexposed to heat, without irradiation, at higher temperatures, forexample, higher than 100° C., or higher. Thus, such formulations, whichare non-reactive or partially-reactive towards to hardening when exposedto a first curing condition which is irradiation, can undergo hardeningwhen exposed to a second condition which is heat.

The following describes exemplary curable materials and formulationssystems comprising same, which are suitable for use in embodiments ofthe present invention.

According to some embodiments of the present invention, at least one ofthe first and second formulations provides a transparent material whenhardened. An exemplary such formulation is prepared and marketed by thepresent assignee under the trade name VeroClear™.

In some of these embodiments, a formulation system comprises the firstand second formulations as described herein and both provide, whenhardened, a transparent material. Such a formulation system is anexemplary formulation system IIa as described herein, and can comprise,in some embodiments, the known transparent formulations as the firstformulation, and, as the second formulation, a formulation thatcomprises the same curable materials but a low amount of aphotoinitiator, as described herein.

According to some embodiments of the present invention, the secondbuilding material formulation comprises a curable material that exhibitsvolume shrinkage during the additive manufacturing process.

When curable materials that exhibit volume shrinkage during AM are usedin a modeling material formulation for an AM process and the shrinkageis significant, the object tends to deform and curl up during theprinting process. This may lead to skewing of the object geometry anddetachment of the object from the surface on which it is printed and maycause an obstruction to the path of the print heads that deposit themodel material. Striking of the print heads with the curled portion ofthe object may damage the print head. A degree of shrinkage may bedefined with a threshold on a ratio of the volume of un-polymerizedmaterial over the volume of the polymerized material. In some examples,volume shrinkage can reach up to 20% (e.g., for some acrylic material).

The curling may be due to gradients in temperature that lead togradients in degree of polymerization along the Z axis. Although, eachlayer deposited during the AM process is separately cured or hardened,the curing or hardening of a given layer may continue as one or moresubsequent layers are added over the given layer. The continued curingor hardening may be due to penetration of curing radiation throughlayers and may also be due thermal energy that may accumulate in theobject based on repeated curing or hardening of layers, based on anexothermic curing or hardening process, as well as based on atemperature at which the material is deposited. Temperature on an uppersurface of a stack of layers may rise as additional layers are addeduntil a steady state temperature is reached. Such temperature gradientstend to appear in the first number of layers deposited. In some examplesystems, steady state may be reached at or around 70° C., e.g. 60°C.-75°. This temperature may be reached at a height of 7-10 mm dependingon the geometry of the printed portion of the object, parameters of thehardened material and parameters of the curing. When upper layers arewarmer and experience a higher degree of curing or hardening as comparedto the lower layers, the upper layers tend to shrink more as compared tothe lower layers. The degree of curling may depend on gradient ofshrinkage along the Z axis.

Glass transition temperature (Tg) may be used as a parameter to defineexpected curling during an AM process. Optionally, HDT may beadditionally or alternatively used as the parameter to define expectedcurling during an AM process. Curling may occur when the material thatis hardened by a curing process has a glass transition temperature (Tg)that is above the steady state temperature of the printed object, e.g.above 70° C. In such cases the polymer may not be able to relax itsinternal stresses at the steady state temperature. This may lead tocurling. To alleviate the stresses additional thermal energy, in a formof heated tray, turning off the cooling fans, and/or heating with IRlamp may be required. However, raising the temperature may adverselyaffect the thermal stability of the dispensed formulation(s) and may attimes lead to evaporation of the curable materials before curing orhardening takes place. For at least this reason, raising the temperatureduring the AM process may not be practical solution.

Curable materials that form, when hardened, a material with Tg that fallbelow the steady state temperature of the printed object do allowcrawling and relaxation of internal stresses and therefore are not proneto shrinking.

According to some example embodiments, curling and/or deformation ofmaterials with relatively high Tg and/or HDT is reduced or avoided byonly partially curing or hardening at least a portion of the materialduring printing to obtain a green body object, and then completing thefabrication of the object by thermal post treatment.

As used herein, HDT refers to a temperature at which the respectiveformulation or combination of formulations deforms under a predeterminedload at some certain temperature. Suitable test procedures fordetermining the HDT of a formulation or combination of formulations arethe ASTM D-648 series, particularly the ASTM D-648-06 and ASTM D-648-07methods. In various exemplary embodiments of the invention the core andshell of the structure differ in their HDT as measured by the ASTMD-648-06 method as well as their HDT as measured by the ASTM D-648-07method. In some embodiments of the present invention the core and shellof the structure differ in their HDT as measured by any method of theASTM D-648 series. In the majority of the examples herein, HDT at apressure of 0.45 MPa was used.

Herein, “Tg” of a material refers to glass transition temperaturedefined as the location of the local maximum of the E″ curve, where E″is the loss modulus of the material as a function of the temperature.

Broadly speaking, as the temperature is raised within a range oftemperatures containing the Tg temperature, the state of a material,particularly a polymeric material, gradually changes from a glassy stateinto a rubbery state.

Herein, “Tg range” is a temperature range at which the E″ value is atleast half its value (e.g., can be up to its value) at the Tgtemperature as defined above.

Without wishing to be bound to any particular theory, it is assumed thatthe state of a polymeric material gradually changes from the glassystate into the rubbery within the Tg range as defined above. The lowesttemperature of the Tg range is referred to herein as Tg(low) and thehighest temperature of the Tg range is referred to herein as Tg(high).

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a heat distortion temperature (HDT) and/or Tgabove a steady state temperature of the plurality of layers during theAM process.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a heat distortion temperature (HDT) and/or Tgabove 70° C.

According to some of any of the embodiments described herein, the firstbuilding material formulation comprises a first curable materialfeaturing, when hardened, a heat distortion temperature (HDT) and/or Tgbelow a steady state temperature of the plurality of layers during theAM process.

According to some of any of the embodiments described herein the firstbuilding material formulation comprises a first curable materialfeaturing, when hardened, a heat distortion temperature (HDT) and/or Tgbelow 70° C.

According to some of any of the embodiments described herein, the secondbuilding material formulation comprises a second curable materialfeaturing, when hardened, a heat distortion temperature (HDT) and/or Tgabove a steady state temperature of the plurality of layers during theAM process (e.g., above 70° C.), and the first building materialformulation comprises a first curable material featuring, when hardened,a heat distortion temperature (HDT) and/or Tg below a steady statetemperature of the plurality of layers during the AM process (e.g.,below 70° C.).

Exemplary curable materials that provide hardened materials that exhibitvolume shrinkage include, but are not limited to, cyanate esters,polyimide precursors (e.g., bismalimides), multi-functional acrylicmaterials, or other polymerizable systems that include C═C double bondopening during polymerization.

In some of any of the embodiments as described herein for materials thatexhibit volume shrinkage, a formulation system I as described herein isusable. In example embodiments, the first formulation comprisesacrylic-based UV-curable material(s), and the first curing conditioncomprises UV-irradiation, and the second formulation comprises asub-formulation A which comprises acrylic-base curable material(s),preferably multi-functional acrylic-based UV-curable materials, and asub-formulation B which comprises thermally-curable materials, forexample, a cyanate ester. In some of these embodiments, an exemplaryformulation system Ia as described herein is used.

In some of any of the embodiments as described herein for materials thatexhibit volume shrinkage, a formulation system as described herein forexemplary formulation system Ic is usable. In some of these embodiments,both the first and second formulations comprise UV-curable acrylic-basedmaterials, while the second formulation comprises acrylic-basedmaterials that provide, when hardened, a material that exhibits high HDTand/or Tg, as described herein.

In some of any of the embodiments described herein for materials thatexhibit volume shrinkage, a formulation system as described herein forexemplary formulation system IIa is usable. In some of theseembodiments, both the first and second formulations comprise a polyimideprecursor (e.g., a bismaleimide) in combination with a reactive diluent,whereby the second formulation comprises a low amount of initiator, asdescribed herein.

Polyimide precursors typically include one or more imide moieties andone or more polymerizable moieties.

An imide moiety is a group that consists of two acyl groups bound to anitrogen atom, —C(═O)—NRa—C(═O)—, wherein Ra can be, for example,hydrogen, alkyl, cycloalkyl, aryl, alkaryl, and any other substituent asdefined herein for other chemical groups.

Exemplary polyimide precursors that are usable in the context of thepresent embodiments include, without limitation, α,ω-bismaleimides(BMIs).

α,ω-Bismaleimides feature two imide moieties which are linked to oneanother via a linking moiety and which further feature polymerizablemoieties that undergo homopolymerization and/or copolymerization whenexposed to UV irradiation, thermal energy and/or chemical catalysis, tothereby provide a cross-linked polyimide.

α,ω-Bismaleimides usable in the context of the present embodiments canbe collectively represented by Formula I:

wherein:

L is a linking moiety which can be, or comprise, an alkyl, an aryl, acycloalkyl, a hydrocarbon, as these terms are defined herein, or,alternatively, a heteroalicyclic, a heteroaryl, a poly(alkylene chain)and any combination of the foregoing; and

R₁-R₄ are each independently selected from hydrogen, alkyl, cycloalkyland optionally any other substituent as described herein.

Preferably, R₁-R₄ are each hydrogen.

The chemical composition and molecular weight of the linking moiety Ldetermine the properties of the obtained polyimide.

In some embodiments, the L linking moiety is a hydrocarbon, as definedherein. In some embodiments, the hydrocarbon consists of one or morealkylene chains. In some embodiments, the hydrocarbon comprises two ormore alkylene chains that are connected therebetween via a branchingunit. In some embodiments, the branching unit comprises or consists of acycloalkyl.

In some embodiments, the L linking moiety is represented by the Formula:

A1-B-A2

wherein A1 and A2 are each an alkylene chain and B is a branching unit.In some embodiments, B is a cycloalkyl, for example, a cyclohexyl, whichis further substituted by one or more alkylene chains.

In some embodiments, A1 and A2 and optional alkylene chains substitutingthe cycloalkyl are each independently of 3 to 20 carbon atoms in length,or of 3 to 15, or of 3 to 10, or of 5 to 10, carbon atoms in length.

The term “branching unit” as used herein describes a multi-radical,preferably aliphatic or alicyclic group. By “multi-radical” it is meantthat the linking moiety has two or more attachment points such that itlinks between two or more atoms and/or groups or moieties.

In some embodiments, the branching unit is derived from a chemicalmoiety that has two, three or more functional groups. In someembodiments, the branching unit is a branched alkyl or is a cycloalkylas defined herein.

In some of any of the embodiments described herein, the linking moietyis selected such that the molecular weight of the BMI is in the range offrom 200 to 5000 Daltons, preferably from 300 to 2000 Daltons, or from300 to 1000 Daltons, of from 500 to 1000 Daltons.

An exemplary BMI includes BMI-689, having a molecular weight of 689Daltons.

A formulation or formulation system (a combination of two or moresub-formulations) that comprises a polyimide precursor can furthercomprise an additional curable material, for example, a mono-functionalor multi-functional acrylic material, as described herein, and/or anorganic solvent.

Exemplary curable materials usable in combination with a polyimideprecursor are described, for example, in WO 2019/130312 and WO2019/130310.

Non-limiting examples of mono-functional acrylates include isobornylacrylate (IBOA), isobornylmethacrylate, acryloyl morpholine (ACMO),phenoxyethyl acrylate, marketed by Sartomer Company (USA) under thetrade name SR-339, urethane acrylate oligomer such as marketed under thename CN 131B, and any other acrylates and methacrylates usable in AMmethodologies.

Non-limiting examples of multi-functional (meth)acrylates includepropoxylated (2) neopentyl glycol diacrylate, marketed by SartomerCompany (USA) under the trade name SR-9003, DitrimethylolpropaneTetra-acrylate (DiTMPTTA), Pentaerythitol Tetra-acrylate (TETTA), andDipentaerythitol Penta-acrylate (DiPEP), and an aliphatic urethanediacrylate, for example, such as marketed as Ebecryl 230. Non-limitingexamples of multi-functional (meth)acrylate oligomers includeethoxylated or methoxylated polyethylene glycol diacrylate ordimethacrylate, ethoxylated bisphenol A diacrylate, polyethyleneglycol-polyethylene glycol urethane diacrylate, a partially acrylatedpolyol oligomer, polyester-based urethane diacrylates such as marketedas CNN91.

Curable materials usable in the context of embodiments related to D-ABSformulation system are described, for example, in WO 2018/055521 and WO2018/055522, which are incorporated by reference as if fully set forthherein.

The phrase “cyanate ester” encompasses one or more cyanate estercompound(s) and/or one or more prepolymer(s) thereof, includinghomoprepolymer(s) and/or heteroprepolymer(s).

The prepolymers comprise a cyanate ester that is polymerized to a degreeof conversion of the cyanate groups of from 1 or 5 percent to 20 or 40percent (of the initial cyanate functionality), leading to prepolymerswith molecular weights of from 200 or 400 g/mol to 4,000 or 8,000 g/mol.

Cyanate ester compounds that are usable in the context of some of thepresent embodiments, as described herein, can be collectivelyrepresented by the following Formula:

R

O—C≡N)_(m)

wherein:

m is an integer of from 1 to 6, and can be, for example, 1, 2, 3, 4, 5or 6, preferably, 2, 3, 4 or 5, more preferably 2 or 3, for example 2;and

R is alkyl, cycloalkyl, aryl, heteroaryl, or heteroalicyclic.Alternatively, R is a hydrocarbon (saturated or unsaturated) that isoptionally interrupted and/or substituted by one or more heteroatomssuch as Si, P, S, O, N.

In some embodiments, R is an aryl, for example, phenyl, naphthyl,anthryl, phenanthryl, or pyrenyl group, each being substituted orunsubstituted.

In some embodiments, R is an aryl such as phenyl, biphenyl, naphthyl,bis(phenyl)methane, bis(phenyl)ethane, bis(phenyl)propane,bis(phenyl)butane, bis(phenyl)ether, bis(phenyl)thioether,bis(phenyl)sulfone, bis(phenyl) phosphine oxide, bis(phenyl)silane,bis(phenyl)hexafluoropropane, bis(phenyl) trifluoroethane, orbis(phenyl)dicyclopentadiene, or a phenol formaldehyde resin, each beingunsubstituted or substituted by, for example, 1-6 substituents.

Exemplary cyanate ester compounds include, but are not limited to, 1,3-,or 1,4-dicyanatobenzene; 1,3,5-tricyanatobenzene; 1,3-, 1,4-, 1,6-,1,8-, 2,6- or 2,7-dicyanatonaphthalene; 1,3,6-tricyanatoaphthalene; 2,2′or 4,4′-dicyanatobiphenyl; bis(4-cyanathophenyl) methane;2,2-bis(4-cyanatophenyl) propane; 2,2-bis(3,5-dichloro-4-cyanatophenyl(propane. 2,2-bis(3-dibromo-4-dicyanatophenyl)propane;bis(4-cyanatophenyl)ether; bis(4-cyanatophenyl)thioether;bis(4-cyanatophenyl) sulfone; tris(4-cyanatophenyl)phosphite;tris(4-cyanatophenyl) phosphate; bis(3-chloro-4-cyanatophenyl)methane:4-cyanatobiphenyl; 4-cumyl cyanato benzene;2-tert-butyl-1,4-dicyanatobenzene; 2,4-dimethyl-1,3-dicyanatobenzene;2,5-di-tert-butyl-1,4-dicyanatobenzene;tetramethyl-1,4-dicyanatobenzene; 4-chloro-1,3-dicyanatobenzene;3,3′,5,5′-tetramethyl-4,4′ dicyanatodiphenyl;bis(3-chloro-4-cyanatophenyl)methane; 1,1,1-tris(4-cyanatophenyl)ethane; 1,1-bis(4-cyanatophenyl)ethane;2,2-bis(3,5-dichloro-4-cyanatophenyl)propane;2,2-bis(3,5-dibromo-4-cyanatophenyl)propane; bis(p-cyanophenoxyphenoxy)benzene; and any mixture of the foregoing.

A cyanate ester of formula I in which m is 2 typically undergoespolymerization by forming a polycyanurate of the formula:

with R being as defined hereinabove.

When the second building material formulation comprises a cyanate ester,it preferably further comprises an agent for promoting polymerization ofthe cyanate ester, and, as described hereinabove, the agent is includedin a sub-formulation that does not include the cyanate ester.

Agents for promoting polymerization of a cyanate ester are known in theart and all are suitable for use in the context of the presentembodiments.

Exemplary such agents include compounds that comprise one or morenucleophilic groups.

According to some of any of the embodiments described herein, the agentfor promoting polymerization of the cyanate ester is inactive(non-active, non-reactive) or is partially active (partially reactive)towards promoting polymerization of the cyanate ester prior to beingexposed to the second curing condition.

According to some embodiments, the agent for promoting polymerization ofthe cyanate ester is activatable by exposure to the first curingcondition and/or to the second curing condition.

According to some embodiments, the agent for promoting polymerization ofthe cyanate ester is activatable by exposure to the first curingcondition and to the second curing condition.

According to some embodiments of the present invention, an agent thatpromotes polymerization of the first curable material (a cyanate ester)is a nucleophile, that is, a compound that comprises a nucleophilicgroup that is reactive towards cyanate ester. Exemplary nucleophilicgroups include amines, thiolates, hydroxides, alkoxides, etc.

In exemplary embodiments, the agent that promotes polymerization of thefirst curable material is a thiol compound, that is, a compound thatcomprises one or more thiol groups.

As is known in the art, thiols can be activated to form a thiolate,which is a reactive nucleophilic species in the polymerization ofcyanate esters.

In some embodiments, the thiol compound comprises one or more thiolgroups attached to one or more carbon atoms, and these one or morecarbon atoms are further substituted by e.g., an alkyl such as methyl.

Exemplary thiol compounds are those belonging to the family marketedunder the trade name Karenz.

In some embodiments, a curable system of a cyanate ester that comprisesa thiol compound as an agent that promotes polymerization of a cyanateester, preferably further comprises an agent for generating a thiolatespecies.

In some embodiments, such an agent is a base, for example, an amine,preferably a tertiary amine.

In some embodiments, the agent that generates a thiolate is a photobase,which generates a base upon exposure to irradiation. An exemplaryphotobase is such that generates a base such as a tertiary amine uponexposure to irradiation.

In some embodiments, the second building material formulation comprisesa cyanate ester as described herein, a thiol as an agent that promotespolymerization of a cyanate ester and a base for activating the thiol bygenerating a thiolate. In some of these embodiments, the cyanate esterand the base are included in one sub-formulation and the thiol isincluded in another sub-formulation.

In some of these embodiments, the base is a photobase that generates atertiary amine when exposed to irradiation.

A thiol is an example of an agent for promoting polymerization of thecyanate ester that is activatable by exposure to the first curingcondition (when a thiolate group is generated) and to the second curingcondition (when the thiolate promotes the polymerization).

In exemplary embodiments, the agent that promotes polymerization of thefirst curable material is an amine, that is, a compound that comprisesone or more amine groups.

The amine can be an aromatic or non-aromatic (aliphatic or alicyclic)amine.

The amine can be a primary, secondary or tertiary amine, and ispreferably primary or secondary amine.

In some embodiments, the amine is an aromatic amine, comprising an arylsubstituted by one or more amine groups and/or by one or moresubstituents that comprise an amine group, collectively referred toherein as amine-containing substituents, and optionally by one or moreadditional substituents. Each of the amine-containing substituent(s) canbe independently a primary or secondary amine.

Exemplary aromatic amines are marketed under the trade name Ethacure 100LC (primary amines), Ethacure 320 (primary amines) and Ethacure 420(secondary amines).

In some embodiments, the amine is a secondary amine.

In some embodiments, the amine is a secondary aromatic amine, whichcomprises an aryl substituted by one or more amine-containingsubstituents, wherein one or more of the amine-containing substituentsis a secondary amine.

An amine (e.g., as described herein) is active towards polymerization ofa cyanate ester when exposed to heat, e.g., to a temperature of 80° C.or more.

An amine (e.g., an aromatic amine) is an example of an agent forpromoting polymerization of the cyanate ester that is activatable byexposure to the second curing condition.

In some embodiments, a second building formulation comprises a cyanateester as described herein, and an amine (e.g., an aromatic amine) as anagent that promotes polymerization of a cyanate ester. The cyanate esteris included in one sub-formulation and the amine is included in anothersub-formulation.

In some of any of the embodiments described herein, the agent thatpromotes polymerization of the cyanate ester is inactive or is partiallyactive, towards polymerization, as defined herein, when exposed to thefirst curing condition. In some embodiments, when the agent isactivatable upon exposure to the first curing condition, it stillremains inactive or partially active towards polymerization of thecyanate ester before being exposed to the second curing condition.

According to some of the present embodiments, the cyanate ester curablesystem is selected such that when the cyanate ester compound, the agentthat promotes polymerization thereof and the agent that activates it, ifpresent, contact one another and exposed to the first curing condition,polymerization of no more than 30%, or no more than 20% or no more than10% of the cyanate ester occurs.

In some of any of the embodiments described herein, the agent thatpromotes polymerization of the cyanate ester is active towards thepolymerization upon exposure to heat (heat energy), e.g., to elevatedtemperature as described herein (e.g., above 80° C. or above 100° C.).

In some of any of the embodiments described herein the second buildingmaterial formulation that comprises a cyanate ester curable systemfurther comprises another curable system which is a photocurable system,for example, a UV-curable system. The second curable system comprises aphotocurable material, for example, a UV-curable material.

In some embodiments, the second curable system further comprises anagent that promotes polymerization of the UV-curable material. Inexemplary embodiments, this agent is a photoinitator.

In some of any of the embodiments described herein, the agent thepromotes polymerization of the UV-curable material is included in onesub-formulation and the UV-curable material is included in anothersub-formulation.

In some of any of the embodiments described herein, one sub-formulationcomprises a cyanate ester material and a photoinitiator and anothersub-formulation comprises a UV-curable material and the agent thatpromotes polymerization of the cyanate ester. In some of theseembodiments, the first sub-formulation further comprises an agent thatactivates the agent that promotes hardening of the cyanate ester.

In some of any of the embodiments described herein, the agent thatpromotes polymerization of the UV-curable material is inactive or ispartially active, as defined herein, towards polymerization of thecyanate ester.

Exemplary such agents are devoid of a group that is active towardspolymerization of the cyanate ester at the jetting temperature asdescribed herein. In exemplary embodiments, such agents are devoid of anucleophilic group as described herein. In some embodiments, it isdevoid of a tertiary amine, and/or hydroxy and/or thiol and/orthioether. In some embodiments, it is devoid of hydroxy.

Exemplary photoinitators that are usable in the context of the presentembodiments are described in the Examples section that follows.

In some embodiments, a UV-curable system comprises acrylic compoundsand/or other photocurable materials that are polymerizable byfree-radical polymerization and the photoinitiator is a free-radicalphotoinitiator.

A free-radical photoinitiator may be any compound that produces a freeradical on exposure to radiation such as ultraviolet or visibleradiation and thereby initiates a polymerization reaction of the acrylicmaterial, as long as it does not include, generate or require anucleophile as described herein, and is preferably soluble in thecyanate ester.

Exemplary photoinitiators include benzophenones, aromatic α-hydroxyketones, benzylketals, aromatic α-aminoketones, phenylglyoxalic acidesters, mono-acylphosphinoxides, bis-acylphosphinoxides,tris-acylphosphinoxides and/or oximesters derived from aromatic ketones.

Exemplary photoinitiators include, but are not limited to, camphorquinone; benzophenone, benzophenone derivatives, such as2,4,6-trimethylbenzophenone, 2-methylbenzophenone,3-methylbenzo-phenone, 4-methylbenzophenone,2-methoxycarbonylbenzophenone 4,4′-bis(chloromethyl)-benzophenone,4-chlorobenzophenone, 4-phenylbenzophenone,3,3′-dimethyl-4-methoxy-benzophenone,[4-(4-methylphenylthio)phenyl]-phenylmethanone,methyl-2-benzoyl-benzoate, 3-methyl-4′-phenylbenzophenone,2,4,6-trimethyl-4′-phenylbenzophenone,4,4′-bis(dimethylamino)benzophenone, 4,4′-bis(diethylamino)benzophenone;thioxanthones, thioxanthone derivatives, polymeric thio-xanthones as forexample OMNIPOL TX; ketal compounds, as for example benzyldimethyl-ketal(IRGACURE® 651); acetophenone, acetophenone derivatives, for exampleα-hydroxy-cycloalkyl phenyl ketones or α-hydroxyalkyl phenyl ketones,such as for example 2-hydroxy-2-methyl-1-phenyl-propanone (DAROCUR®1173), 1-hydroxy-cyclohexyl-phenyl-ketone (IRGACURE® 184),1-(4-dodecylbenzoyl)-1-hydroxy-1-methyl-ethane,1-(4-isopropylbenzoyl)-1-hydroxy-1-methyl-ethane,1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one(IRGACURE® 2959);2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one(IRGACURE® 127);2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propion-yl)-phenoxy]-phenyl}-2-methyl-propan-1-one;dialkoxyacetophenones, α-hydroxy- or α-am-inoacetophenones, e.g.,(4-methylthiobenzoyl)-1-methyl-1-morpholinoethane (IRGACURE® 907),(4-morpholinobenzoyl)-1-benzyl-1-dimethylaminopropane (IRGACURE® 369),(4-morpholinobenzoyl)-1-(4-methylbenzyl)-1-dimethylaminopropane(IRGACURE® 379),(4-(2-hydroxyethyl)aminobenzoyl)-1-benzyl-1-dimethylaminopropane),(3,4-dimethoxybenzoyl)-1-benzyl-1-dimethyl aminopropane;4-aroyl-1,3-dioxolanes, benzoin alkyl ethers and benzyl ketals, e.g.dimethyl benzyl ketal, phenylglyoxalic esters and derivatives thereof,e.g., methyl α-oxo benzeneacetate, oxo-phenyl-acetic acid2-(2-hydroxy-ethoxy)-ethyl ester, dimeric phenylglyoxalic esters, e.g.oxo-phenyl-acetic acid1-methyl-2-[2-(2-oxo-2-phenyl-acetoxy)-propoxy]-ethyl ester (IRGACURE®754); ketosulfones, e.g. ESACURE KIP 1001 M®; oxime-esters, e.g.,1,2-octanedione 1-[4-(phenylthio)phenyl]-2-(O-benzoyloxime) (IRGACURE®OXE01), ethanone1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime)(IRGACURE® OXE02), 9H-thioxanthene-2-carboxaldehyde9-oxo-2-(O-acetyloxime), peresters, benzophenone tetracarboxylicperesters, monoacyl phosphine oxides, e.g.(2,4,6-trimethylbenzoyl)diphenylphosphine oxide (DAROCUR® TPO),ethyl(2,4,6 trimethylbenzoyl phenyl)phosphinic acid ester;bisacyl-phosphine oxides, e.g.,bis(2,6-dimethoxy-benzoyl)-(2,4,4-trimethyl-pentyl)phosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (IRGACURE® 819),bis(2,4,6-trimethyl-benzoyl)-2,4-dipentoxyphenylphosphine oxide,trisacylphosphine oxides, halomethyltriazines, e.g.,2-[2-(4-methoxy-phenyl)-vinyl]-4,6-bis-trichloromethyl-[1,3,5]triazine,2-(4-methoxy-phenyl)-4,6-bis-trichloromethyl-[1,3,5]triazine,2-(3,4-dimethoxy-phenyl)-4,6-bis-trichlorome-thyl-[1,3,5]triazine,2-methyl-4,6-bis-trichloromethyl-[1,3,5]triazine,hexaarylbisimidazole/coinitiators systems, e.g.,ortho-chlorohexaphenyl-bisimidazole combined with2-mercapto-benzthiazole, ferrocenium compounds, or titanocenes, e.g.,bis(cyclopentadienyl)-bis(2,6-difluoro-3-pyrryl-phenyl)titanium(IRGACURE®784).

Exemplary alpha-hydroxy ketone PIs include, but are not limited to,1-hydroxy-cyclohexyl-phenyl-ketone (IRGACURE® 184, I-184),2-hydroxy-1-{1-[4-(2-hydroxy-2-methyl-propionyl)-phenyl]-1,3,3-trimethyl-indan-5-yl}-2-methyl-propan-1-one,(ESACURE ONE®), and1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one(IRGACURE® 2959, 1-2959).

According to some of any of the embodiments described herein, thephotoinitiator(s) comprises, or consists essentially of, a phosphineoxide-type (e.g., mono-acylated or bis-acylated phosphine oxide-type;BAPO or BPO) photoinitiator.

Exemplary monoacyl and bisacyl phosphine oxides include, but are notlimited to, 2,4,6-trimethylbenzoyldiphenyl phosphine oxide,bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide,dibenzoylphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)phenylphosphine oxide, tris(2,4-dimethylbenzoyl) phosphine oxide,tris(2-methoxybenzoyl)phosphine oxide, 2,6-dimethoxybenzoyldiphenylphosphine oxide, 2,6-dichlorobenzoyldiphenyl phosphine oxide,2,3,5,6-tetramethylbenzoyldiphenyl phosphine oxide,benzoyl-bis(2,6-dimethylphenyl) phosphonate, and2,4,6-trimethylbenzoylethoxyphenyl phosphine oxide. Commerciallyavailable phosphine oxide photoinitiators capable of free-radicalinitiation when irradiated at wavelength ranges of greater than about380 nm to about 450 nm include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (IRGACURE 819),bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (CGI403), a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE 1700), a 1:1 mixture,by weight, of bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR 4265), and ethyl2,4,6-trimethylbenzylphenyl phosphinate (LUCIRIN LR8893X).

Non-limiting examples of photoinitiators include acylphosphine oxidetype photo-initiators such as 2,4,6-trimethylbenzolydiphenyl phosphineoxide (TMPO), 2,4,6-trimethylbenzoylethoxyphenyl phosphine oxide (TEPO),and bisacylphosphine oxides (BAPO's); benzoins and bezoin alkyl etherssuch as benzoin, benzoin methyl ether and benzoin isopropyl ether andthe like. Examples of photoinitiators are alpha-amino ketone, andbisacylphosphine oxide (BAPO's). Further examples includephotoinitiators of the Irgacure® family.

In some of any of the embodiments described herein the UV-curablematerial is selected such that is provides, when hardened, a Tg of atleast 150° C.

In some of any of the embodiments described herein, the UV-curablematerial comprises one or more, multi-functional curable materials.

In some of any of the embodiments described herein, the UV-curablematerial comprises one or more, multi-functional curable materials andat least one of these materials provides, when hardened, a Tg of atleast 150° C.

In some of any of the embodiments described herein, the second curablematerial comprises one or more multi-functional curable materials andthe type and amount of these materials are selected to provide, whenhardened, an average Tg of at least 150° C.

Herein throughout, an average Tg means a sum of the Tg of each componentmultiplied by its relative weight portion divided by the sum of therespective weight portions.

For example, if material A is included in an amount of X weight percentand features Tg1, and a material B is included in an amount of Y weightpercent and features Tg2, then an average Tg of materials A and B iscalculated herein as:

Average Tg=(X×Tg1+Y×Tg2)/X+Y.

Exemplary difunctional curable materials which are usable in the contextof the present embodiments are collectively represented by the followingFormula:

wherein:

X is selected from —O— and —O—C(═O)—; D is a hydrocarbon as definedherein in any of the respective embodiments; and

Rx and Ry are each independently selected from hydrogen, alkyl andcycloalkyl.

When X is O, the difunctional curable material is a divinyl ether.

When X is —O—C(═O)— the difunctional curable material is adi(meth)acrylate.

When X is —O—C(═O)— and Rx and Ry are each hydrogen, the difunctionalmaterial is a diacrylate.

When X is —O—C(═O)— and Rx and Ry are each methyl, the difunctionalmaterial is a dimethacrylate.

In some of any of the embodiments described herein, the difunctionalcurable material is a divinyl ether as depicted in Formula II.

In some of any of the embodiments described herein, the difunctionalcurable material is a dimethacrylate as depicted in Formula II.

In some of any of the embodiments defined herein, the hydrocarbon is orcomprises a rigid moiety, for example, a cyclic moiety such as acycloalkyl (an alicyclic moiety) and/or an aryl (e.g., phenyl) oralkaryl (e.g., benzyl).

Non-limiting examples of multi-functional (meth)acrylates includepropoxylated (2) neopentyl glycol diacrylate, marketed by SartomerCompany (USA) under the trade name SR-9003, DitrimethylolpropaneTetra-acrylate (DiTMPTTA), Pentaerythitol Tetra-acrylate (TETTA),Dipentaerythitol Penta-acrylate (DiPEP), and an aliphatic urethanediacrylate, for example, such as marketed as Ebecryl 230, ethoxylated ormethoxylated polyethylene glycol diacrylate or dimethacrylate,ethoxylated bisphenol A diacrylate, polyethylene glycol-polyethyleneglycol urethane diacrylate, a partially acrylated polyol oligomer,polyester-based urethane diacrylates such as marketed as CNN91.

Examples of multi-functional (meth)acrylates that feature a Tg higherthan 150° C. and are usable in the context of the respective embodimentsinclude, but are not limited to, materials marketed by Sartomer underthe trade names SR834, SR444D, SR368, SR833s, SR351, SR355 and SR299.Other materials are also contemplated.

In some embodiments, the UV-curable material comprises a di-functionalacrylic material, preferably a di-functional acrylate or methacrylate.

In some embodiments, the UV-curable material comprises a di-functionalacrylic material, preferably a di-functional acrylate or methacrylate,and another multi-functional acrylate or methacrylate, such as atri-functional or tetra-functional acrylate or methacrylate.

In some of these embodiments, a weight ratio of the di-functionalacrylate or methacrylate and the other multi-functional acrylate ormethacrylate ranges from about 10:1 to 2:1, including any intermediatevalue and subranges therebetween.

The UV-curable material can alternatively be monofunctional or compriseone or more monofunctional curable materials such as monofunctionalacrylates and/or methacrylates.

In some of any of the embodiments described herein, an amount of theagent that promotes polymerization of the cyanate ester ranges fromabout 5 to 25, or from about 8 to about 20, weight percents of the totalweight of the second formulation or of the sub-formulation containingsame, including any intermediate values and subranges therebetween.

In some of any of the embodiments described herein, an amount of theagent that promotes polymerization of the UV-curable material in thesub-formulation containing same ranges from about 1 to about 5 weightpercents of the total weight of the formulation, including anyintermediate values and subranges therebetween.

Formulation systems that comprise a cyanate ester may include, as anagent that promotes polymerization of the cyanate ester, a metalspecies, which is also referred to herein as a metal catalyst, insteadof or in addition to a thiol or amine compound as described herein.

Any metal-based material that is known in the art to promotepolymerization of a cyanate ester (as a metal catalyst) is contemplated.These include, for example, a chelate or oxide of a metal such ascopper, zinc, manganese, tin, lead, cobalt, nickel, iron, aluminum, ortitanium, or a metal salt of an organic acid, of which the metal iscopper, zinc, lead, nickel, iron, tin, or cobalt.

The metal species is preferably not included in the formulation orsub-formulation that comprises the cyanate ester.

An exemplary metal species comprises a complex of zinc ions and anorganic moiety, preferably a hydrophobic moiety.

In some embodiments, an amount of the metal species (metal catalyst)ranges from about 0.01 to about 0.5% by weight, or from about 0.01 toabout 0.2% by weight, of the total weight of the formulation containingsame.

Formulation systems that comprise a cyanate ester can further include anadditional curable material which is capable of interacting with thecyanate ester to thereby form a co-polymeric network.

In some of these embodiments the additional curable material is capableof interacting with the cyanate ester upon exposure to the first and/orthe second curing condition.

An exemplary such material is an epoxy-containing curable material.

Epoxy-containing curable materials comprise one or more curable epoxygroups which substitute an aromatic, aliphatic or alicyclic moiety.

Herein throughout, “an aromatic moiety” describes a moiety that is orcomprises one or more aryl or heteroaryl groups.

Herein throughout, “an aliphatic moiety” or “non-aromatic moiety”describes a moiety that does not comprise an aryl or heteroaryl group,and which can be non-cyclic or cyclic, in which case it is also referredto herein as an alicyclic moiety.

In some of any of the embodiments described herein, the additionalcurable material features a viscosity lower than 1,000, or lower than500, centipoises, at room temperature.

In some of any of the embodiments described herein, the epoxy-containingcurable material features a viscosity lower than 1,000, or lower than500, centipoises, at room temperature. Exemplary such materials aretypically aliphatic or alicyclic epoxy-containing materials, which canbe mono-functional or multi-functional.

Exemplary epoxy-containing curable materials include, but are notlimited to, Bis-(3,4 cyclohexylmethyl) adipate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexyl carboxylate, 1,2epoxy-4-vinylcyclohexane, 1,2-epoxy hexadecane, 3,4-epoxycyclohexylmethyl-3,4-epoxy cyclohexane carboxylate, which is available,for example, under the trade name UVACURE 1500 from Cytec SurfaceSpecialties SA/NV (Belgium) and mono or multifunctional silicon epoxyresins such as PC 1000 which is available from Polyset Company (USA).

An amount of the additional curable material can be selected as desiredand in accordance with considerations such as the mechanical propertiesof the obtained cyanate ester-containing polymeric network and costs.

In some of these embodiments, a weight ratio of the sub-formulations inthe second building material formulation ranges from about 80:20 toabout 20:80 or from about 70:30 to 30:70, or from about 70:30 to 50:50,including any intermediate values and subranges therebetween.

In some of any of the embodiments described herein, the first and/orsecond building material formulation independently further comprises oneor more additional materials, which are referred to herein also asnon-reactive materials (non-curable materials).

Such materials include, for example, surface active agents(surfactants), inhibitors, antioxidants, fillers, pigments, dyes, and/ordispersants.

Surface-active agents may be used to reduce the surface tension of theformulation to the value required for jetting or for printing process,which is typically around 30 dyne/cm. Such agents include siliconematerials, for example, organic polysiloxanes such as PDMS andderivatives therefore, such as those commercially available as BYK typesurfactants.

Suitable dispersants (dispersing agents) can also be silicone materials,for example, organic polysiloxanes such as PDMS and derivativestherefore, such as those commercially available as BYK type surfactants.

Suitable stabilizers (stabilizing agents) include, for example, thermalstabilizers, which stabilize the formulation at high temperatures.

The term “filler” describes an inert material that modifies theproperties of a polymeric material and/or adjusts a quality of the endproducts. The filler may be an inorganic particle, for example calciumcarbonate, silica, and clay.

Fillers may be added to the modeling formulation in order to reduceshrinkage during polymerization or during cooling, for example, toreduce the coefficient of thermal expansion, increase strength, increasethermal stability, reduce cost and/or adopt rheological properties.Nanoparticles fillers are typically useful in applications requiring lowviscosity such as ink-jet applications.

In some embodiments, a concentration of each of a surfactant and/or adispersant and/or a stabilizer and/or a filler, if present, ranges from0.01 to 2%, or from 0.01 to 1%, by weight, of the total weight of therespective formulation. Dispersants are typically used at aconcentration that ranges from 0.01 to 0.1%, or from 0.01 to 0.05%, byweight, of the total weight of the respective formulation.

In some embodiments, the first and/or second formulation furthercomprises an inhibitor. The inhibitor is included for preventing orreducing curing before exposure to a curing condition. Suitableinhibitors include, for example, those commercially available as the‘Genorad’ type, or as MEHQ. Any other suitable inhibitors arecontemplated.

The pigments can be organic and/or inorganic and/or metallic pigments,and in some embodiments the pigments are nanoscale pigments, whichinclude nanoparticles.

Exemplary inorganic pigments include nanoparticles of titanium oxide,and/or of zinc oxide and/or of silica. Exemplary organic pigmentsinclude nanosized carbon black.

In some embodiments, the pigment's concentration ranges from 0.1 to 2%by weight, or from 0.1 to 1.5%, by weight, of the total weight of therespective formulation.

In some embodiments, combinations of white pigments and dyes are used toprepare colored cured materials.

The dye may be any of a broad class of solvent soluble dyes. Somenon-limiting examples are azo dyes which are yellow, orange, brown andred; anthraquinone and triarylmethane dyes which are green and blue; andazine dye which is black.

In some of any of the embodiments described herein there is provided akit comprising a first formulation and a second formulation (includingsub-formulations A and B) as described herein in any of the respectiveembodiments and any combination thereof.

In some embodiments, each formulation is packaged individually in thekit.

In exemplary embodiments, the formulations are packaged within the kitin a suitable packaging material, preferably, an impermeable material(e.g., water- and gas-impermeable material), and further preferably anopaque material. In some embodiments, the kit further comprisesinstructions to use the formulations in an additive manufacturingprocess, preferably a 3D inkjet printing process as described herein.The kit may further comprise instructions to use the formulations in theprocess in accordance with the method as described herein.

It is expected that during the life of a patent maturing from thisapplication many relevant curable materials and/or respective agents forpromoting polymerization of curable materials will be developed and thescope of the terms first curable material, second curable material andagents promoting polymerization thereof is intended to include all suchnew technologies a priori.

As used herein the term “about” refers to ±10% or ±5%.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration.” Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments.” Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” or “process” refers to manners, means,techniques and procedures for accomplishing a given task including, butnot limited to, those manners, means, techniques and procedures eitherknown to, or readily developed from known manners, means, techniques andprocedures by practitioners of the chemical, pharmacological,biological, biochemical and medical arts.

Herein throughout, the term “(meth)acrylic” encompasses acrylic andmethacrylic materials.

Herein throughout, the phrase “linking moiety” or “linking group”describes a group that connects two or more moieties or groups in acompound. A linking moiety is typically derived from a bi- ortri-functional compound, and can be regarded as a bi- or tri-radicalmoiety, which is connected to two or three other moieties, via two orthree atoms thereof, respectively.

Exemplary linking moieties include a hydrocarbon moiety or chain,optionally interrupted by one or more heteroatoms, as defined herein,and/or any of the chemical groups listed below, when defined as linkinggroups.

When a chemical group is referred to herein as “end group” it is to beinterpreted as a substituent, which is connected to another group viaone atom thereof.

Herein throughout, the term “hydrocarbon” collectively describes achemical group composed mainly of carbon and hydrogen atoms. Ahydrocarbon can be comprised of alkyl, alkene, alkyne, aryl, and/orcycloalkyl, each can be substituted or unsubstituted, and can beinterrupted by one or more heteroatoms. The number of carbon atoms canrange from 2 to 30, and is preferably lower, e.g., from 1 to 10, or from1 to 6, or from 1 to 4. A hydrocarbon can be a linking group or an endgroup.

Bisphenol A is an example of a hydrocarbon comprised of 2 aryl groupsand one alkyl group. Dimethylenecyclohexane is an example of ahydrocarbon comprised of 2 alkyl groups and one cycloalkyl group.

As used herein, the term “amine” describes both a —NR′R″ group and a—NR′— group, wherein R′ and R″ are each independently hydrogen, alkyl,cycloalkyl, aryl, as these terms are defined hereinbelow.

The amine group can therefore be a primary amine, where both R′ and R″are hydrogen, a secondary amine, where R′ is hydrogen and R″ is alkyl,cycloalkyl or aryl, or a tertiary amine, where each of R′ and R″ isindependently alkyl, cycloalkyl or aryl.

Alternatively, R′ and R″ can each independently be hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, carbonyl, C-carboxylate, O-carboxylate,N-thiocarbamate, 0-thiocarbamate, urea, thiourea, N-carbamate,O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine.

The term “amine” is used herein to describe a —NR′R″ group in caseswhere the amine is an end group, as defined hereinunder, and is usedherein to describe a —NR′— group in cases where the amine is a linkinggroup or is or part of a linking moiety.

The term “alkyl” describes a saturated aliphatic hydrocarbon includingstraight chain and branched chain groups. Preferably, the alkyl grouphas 1 to 30, or 1 to 20 carbon atoms. Whenever a numerical range; e.g.,“1-20”, is stated herein, it implies that the group, in this case thealkyl group, may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms,etc., up to and including 20 carbon atoms. The alkyl group may besubstituted or unsubstituted. Substituted alkyl may have one or moresubstituents, whereby each substituent group can independently be, forexample, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl,heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine.

The alkyl group can be an end group, as this phrase is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this phrase is defined hereinabove, which connects twoor more moieties via at least two carbons in its chain. When the alkylis a linking group, it is also referred to herein as “alkylene” or“alkylene chain”.

Alkene and Alkyne, as used herein, are an alkyl, as defined herein,which contains one or more double bond or triple bond, respectively.

The term “cycloalkyl” describes an all-carbon monocyclic ring or fusedrings (i.e., rings which share an adjacent pair of carbon atoms) groupwhere one or more of the rings does not have a completely conjugatedpi-electron system. Examples include, without limitation, cyclohexane,adamantine, norbornyl, isobornyl, and the like. The cycloalkyl group maybe substituted or unsubstituted. Substituted cycloalkyl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The cycloalkyl group can be an end group, as this phrase isdefined hereinabove, wherein it is attached to a single adjacent atom,or a linking group, as this phrase is defined hereinabove, connectingtwo or more moieties at two or more positions thereof.

The term “heteroalicyclic” describes a monocyclic or fused ring grouphaving in the ring(s) one or more atoms such as nitrogen, oxygen andsulfur. The rings may also have one or more double bonds. However, therings do not have a completely conjugated pi-electron system.Representative examples are piperidine, piperazine, tetrahydrofurane,tetrahydropyrane, morpholino, oxalidine, and the like.

The heteroalicyclic may be substituted or unsubstituted. Substitutedheteroalicyclic may have one or more substituents, whereby eachsubstituent group can independently be, for example, hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate,O-thiocarbamate, urea, thiourea, O-carbamate, N-carbamate, C-amide,N-amide, guanyl, guanidine and hydrazine. The heteroalicyclic group canbe an end group, as this phrase is defined hereinabove, where it isattached to a single adjacent atom, or a linking group, as this phraseis defined hereinabove, connecting two or more moieties at two or morepositions thereof.

The term “aryl” describes an all-carbon monocyclic or fused-ringpolycyclic (i.e., rings which share adjacent pairs of carbon atoms)groups having a completely conjugated pi-electron system. The aryl groupmay be substituted or unsubstituted. Substituted aryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The aryl group can be an end group, as this term is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this term is defined hereinabove, connecting two ormore moieties at two or more positions thereof.

The term “heteroaryl” describes a monocyclic or fused ring (i.e., ringswhich share an adjacent pair of atoms) group having in the ring(s) oneor more atoms, such as, for example, nitrogen, oxygen and sulfur and, inaddition, having a completely conjugated pi-electron system. Examples,without limitation, of heteroaryl groups include pyrrole, furan,thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine,quinoline, isoquinoline and purine. The heteroaryl group may besubstituted or unsubstituted. Substituted heteroaryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,O-carbamate, N-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The heteroaryl group can be an end group, as this phrase isdefined hereinabove, where it is attached to a single adjacent atom, ora linking group, as this phrase is defined hereinabove, connecting twoor more moieties at two or more positions thereof. Representativeexamples are pyridine, pyrrole, oxazole, indole, purine and the like.

The term “halide” and “halo” describes fluorine, chlorine, bromine oriodine. The term “haloalkyl” describes an alkyl group as defined above,further substituted by one or more halide.

The term “sulfate” describes a —O—S(═O)₂—OR′ end group, as this term isdefined hereinabove, or an —O—S(═O)₂—O— linking group, as these phrasesare defined hereinabove, where R′ is as defined hereinabove.

The term “thiosulfate” describes a —O—S(═S)(═O)—OR′ end group or a—O—S(═S)(═O)—O— linking group, as these phrases are defined hereinabove,where R′ is as defined hereinabove.

The term “sulfite” describes an —O—S(═O)—O—R′ end group or a —O—S(═O)—O—group linking group, as these phrases are defined hereinabove, where R′is as defined hereinabove.

The term “thiosulfite” describes a —O—S(═S)—O—R′ end group or an—O—S(═S)—O— group linking group, as these phrases are definedhereinabove, where R′ is as defined hereinabove.

The term “sulfinate” describes a —S(═O)—OR′ end group or an —S(═O)—O—group linking group, as these phrases are defined hereinabove, where R′is as defined hereinabove.

The term “sulfoxide” or “sulfinyl” describes a —S(═O)R′ end group or an—S(═O)— linking group, as these phrases are defined hereinabove, whereR′ is as defined hereinabove.

The term “sulfonate” describes a —S(═O)₂—R′ end group or an —S(═O)₂—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “S-sulfonamide” describes a —S(═O)₂—NR′R″ end group or a—S(═O)₂—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-sulfonamide” describes an R'S(═O)₂—NR″— end group or a—S(═O)₂—NR′— linking group, as these phrases are defined hereinabove,where R′ and R″ are as defined herein.

The term “disulfide” refers to a —S—SR′ end group or a —S—S— linkinggroup, as these phrases are defined hereinabove, where R′ is as definedherein.

The term “phosphonate” describes a —P(═O)(OR′)(OR″) end group or a—P(═O)(OR′)(O)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “thiophosphonate” describes a —P(═S)(OR′)(OR″) end group or a—P(═S)(OR′)(O)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “phosphinyl” describes a —PR′R″ end group or a —PR′— linkinggroup, as these phrases are defined hereinabove, with R′ and R″ asdefined hereinabove.

The term “phosphine oxide” describes a —P(═O)(R′)(R″) end group or a—P(═O)(R′)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “phosphine sulfide” describes a —P(═S)(R′)(R″) end group or a—P(═S)(R′)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “phosphite” describes an —O—PR′(═O)(OR″) end group or an—O—PH(═O)(O)— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “carbonyl” or “carbonate” as used herein, describes a —C(═O)—R′end group or a —C(═O)— linking group, as these phrases are definedhereinabove, with R′ as defined herein.

The term “thiocarbonyl” as used herein, describes a —C(═S)—R′ end groupor a —C(═S)— linking group, as these phrases are defined hereinabove,with R′ as defined herein.

The term “oxo” as used herein, describes a (═O) group, wherein an oxygenatom is linked by a double bond to the atom (e.g., carbon atom) at theindicated position.

The term “thiooxo” as used herein, describes a (═S) group, wherein asulfur atom is linked by a double bond to the atom (e.g., carbon atom)at the indicated position.

The term “oxime” describes a ═N—OH end group or a ═N—O— linking group,as these phrases are defined hereinabove.

The term “hydroxyl” describes a —OH group.

The term “alkoxy” describes both an —O-alkyl and an —O-cycloalkyl group,as defined herein. The term alkoxide describes —R′O⁻ group, with R′ asdefined herein.

The term “aryloxy” describes both an —O-aryl and an —O-heteroaryl group,as defined herein.

The term “thiohydroxy” or “thiol” describes a —SH group. The term“thiolate” describes a —S⁻ group.

The term “thioalkoxy” describes both a —S-alkyl group, and a—S-cycloalkyl group, as defined herein.

The term “thioaryloxy” describes both a —S-aryl and a —S-heteroarylgroup, as defined herein.

The “hydroxyalkyl” is also referred to herein as “alcohol”, anddescribes an alkyl, as defined herein, substituted by a hydroxy group.

The term “cyano” describes a —C≡N group.

The term “isocyanate” describes an —N═C═O group.

The term “isothiocyanate” describes an —N═C═S group.

The term “nitro” describes an —NO₂ group.

The term “acyl halide” describes a —(C═O)R″″ group wherein R″″ ishalide, as defined hereinabove.

The term “azo” or “diazo” describes an —N═NR′ end group or an —N═N—linking group, as these phrases are defined hereinabove, with R′ asdefined hereinabove.

The term “peroxo” describes an —O—OR′ end group or an —O—O— linkinggroup, as these phrases are defined hereinabove, with R′ as definedhereinabove.

The term “carboxylate” as used herein encompasses C-carboxylate andO-carboxylate.

The term “C-carboxylate” describes a —C(═O)—OR′ end group or a —C(═O)—O—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “O-carboxylate” describes a —OC(═O)R′ end group or a —OC(═O)—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

A carboxylate can be linear or cyclic. When cyclic, R′ and the carbonatom are linked together to form a ring, in C-carboxylate, and thisgroup is also referred to as lactone. Alternatively, R′ and O are linkedtogether to form a ring in O-carboxylate. Cyclic carboxylates canfunction as a linking group, for example, when an atom in the formedring is linked to another group.

The term “thiocarboxylate” as used herein encompasses C-thiocarboxylateand O-thiocarboxylate.

The term “C-thiocarboxylate” describes a —C(═S)—OR′ end group or a—C(═S)—O— linking group, as these phrases are defined hereinabove, whereR′ is as defined herein.

The term “O-thiocarboxylate” describes a —OC(═S)R′ end group or a—OC(═S)— linking group, as these phrases are defined hereinabove, whereR′ is as defined herein.

A thiocarboxylate can be linear or cyclic. When cyclic, R′ and thecarbon atom are linked together to form a ring, in C-thiocarboxylate,and this group is also referred to as thiolactone. Alternatively, R′ andO are linked together to form a ring in O-thiocarboxylate. Cyclicthiocarboxylates can function as a linking group, for example, when anatom in the formed ring is linked to another group.

The term “carbamate” as used herein encompasses N-carbamate andO-carbamate.

The term “N-carbamate” describes an R″OC(═O)—NR′— end group or a—OC(═O)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “O-carbamate” describes an —OC(═O)—NR′R″ end group or an—OC(═O)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

A carbamate can be linear or cyclic. When cyclic, R′ and the carbon atomare linked together to form a ring, in O-carbamate. Alternatively, R′and O are linked together to form a ring in N-carbamate. Cycliccarbamates can function as a linking group, for example, when an atom inthe formed ring is linked to another group.

The term “carbamate” as used herein encompasses N-carbamate andO-carbamate.

The term “thiocarbamate” as used herein encompasses N-thiocarbamate andO-thiocarbamate.

The term “O-thiocarbamate” describes a —OC(═S)—NR′ R″ end group or a—OC(═S)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-thiocarbamate” describes an R″OC(═S)NR′— end group or a—OC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

Thiocarbamates can be linear or cyclic, as described herein forcarbamates.

The term “dithiocarbamate” as used herein encompasses S-dithiocarbamateand N-dithiocarbamate.

The term “S-dithiocarbamate” describes a —SC(═S)—NR′R″ end group or a—SC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-dithiocarbamate” describes an R″SC(═S)NR′— end group or a—SC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “urea”, which is also referred to herein as “ureido”, describesa —NR′C(═O)—NR″R′″ end group or a —NR′C(═O)—NR″— linking group, as thesephrases are defined hereinabove, where R′ and R″ are as defined hereinand R′″ is as defined herein for R′ and R″.

The term “thiourea”, which is also referred to herein as “thioureido”,describes a —NR′—C(═S)—NR″R′″ end group or a —NR′—C(═S)—NR″— linkinggroup, with R′, R″ and R′″ as defined herein.

The term “amide” as used herein encompasses C-amide and N-amide.

The term “C-amide” describes a —C(═O)—NR′R″ end group or a —C(═O)—NR′—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “N-amide” describes a R′C(═O)—NR″— end group or a R′C(═O)—N—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

An amide can be linear or cyclic. When cyclic, R′ and the carbon atomare linked together to form a ring, in C-amide, and this group is alsoreferred to as lactam. Cyclic amides can function as a linking group,for example, when an atom in the formed ring is linked to another group.

The term “guanyl” describes a R′R″NC(═N)— end group or a —R′NC(═N)—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “guanidine” describes a —R′NC(═N)—NR″R′″ end group or a—R′NC(═N)—NR″— linking group, as these phrases are defined hereinabove,where R′, R″ and R′″ are as defined herein.

The term “hydrazine” describes a —NR′—NR″R′″ end group or a —NR′—NR″—linking group, as these phrases are defined hereinabove, with R′, R″,and R′″ as defined herein.

As used herein, the term “hydrazide” describes a —C(═O)—NR′—NR″R′″ endgroup or a —C(═O)—NR′—NR″— linking group, as these phrases are definedhereinabove, where R′, R″ and R′″ are as defined herein.

As used herein, the term “thiohydrazide” describes a —C(═S)—NR′—NR″R′″end group or a —C(═S)—NR′—NR″— linking group, as these phrases aredefined hereinabove, where R′, R″ and R′″ are as defined herein.

As used herein, the term “alkylene glycol” describes a—O—[(CR′R″)_(z)—O]_(y)R′″ end group or a —O—[(CR′R″)_(z)—O]_(y)— linkinggroup, with R′, R″ and R′″ being as defined herein, and with z being aninteger of from 1 to 10, preferably, from 2 to 6, more preferably 2 or3, and y being an integer of 1 or more. Preferably R′ and R″ are bothhydrogen. When z is 2 and y is 1, this group is ethylene glycol. When zis 3 and y is 1, this group is propylene glycol. When y is 2-4, thealkylene glycol is referred to herein as oligo(alkylene glycol).

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find support inthe following examples.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in anon-limiting fashion.

Materials and Methods

All objects were printed using PolyJet™ Printer available by Stratasys®Ltd., Israel, unless otherwise indicated.

Curling bars as described herein are rectangular objects having thefollowing dimensions: 25×1×1 cm.

RGD515, VeroWhite, and RGD537™ are acrylic-based, UV-curableformulations, prepared and marketed by the present assignee.

Other formulations are described hereinunder.

UV curing was performed using mercury lamp.

Thermal curing was performed in a standard laboratory oven.

Example 1 Formulation Systems Comprising a Cyanate Ester CurableMaterial and an Acrylic Curable Material

An exemplary formulation system comprising a cyanate ester curablematerial (featuring high HDT, as defined herein) and an acrylic curablematerial (featuring high Tg, as defined herein) was used as the secondbuilding material formulation.

This formulation system generally includes two modeling materialsub-formulations as follows: the sub-formulation A comprises acrylicUV-curable materials and an agent that promotes polymerization of acyanate ester, and the sub-formulation B comprises a thermally curablecyanate ester and a photoinitiator that promotes curing of the acrylicmaterials.

Table 1A below presents the composition an exemplary sub-formulation A,and Table 1B below presents the composition of an exemplarysub-formulation B.

TABLE 1A Wt. % Component Aromatic amine-  5-10 containing activator forCE curing Difunctional 65-75 methacrylate monomer (e.g., 70-75)featuring Tg > 150° C. Trifunctional acrylate 10-30 oligomer featuringTg > (e.g., 15-25) 150° C. Surface active agent 0.01-0.1  PropertiesVisc. (68° C.) about 18.5 cP Surface Tension about 29 dyne/cm

TABLE 1B Wt. % Component Cyanate ester resin 95-99 Surface active agent0.05-0.5  (e.g., 0.1-0.3) Photoinitiator 1-2 (e.g., Irgacure369 + ITX-2)Properties Visc. (68° C.) 20.7 cP Surface Tension 28 dyne/cm

The first formulation, forming a shell enveloping the inner region,generally comprises one or more acrylic materials and a photoinitiatorin an amount that renders the formulation active towards hardening whenexposed to UV-irradiation.

Objects were manufactured in accordance with the present embodiments,while dispensing each formulation and sub-formulation from a differentinkjet printhead or a different nozzle, and exposing each of thedispensed layers to UV irradiation as described herein, to therebyobtain green body object having a shell formed with the acrylicmaterials (the first formulation), and a core formed of sub-formulationsA and B, comprising non-cured or partially cured cyanate ester monomersand cured acrylic materials.

The resulted printed green body objects were post cured at elevatedtemperatures, as follows: 2 hours at 100° C., followed by 2 hours at 2hr-150° C., followed by two hours at 200° C., followed by 4 hours at220° C.

FIG. 11A presents a photograph of green body objects that were obtainedwhile using as the second formulation the formulation system describedin Tables 1A and 1B, and as the first formulation the formulationmarketed as RGD515.

FIG. 11B presents a photograph of green body objects that were obtainedwhile using as the second formulation the formulation system describedin Tables 1A and 1B, and as the first formulation the formulationmarketed as RGD515, while being subjected to the second curingcondition.

The final HDT of the printed part is above 250° C.

FIGS. 11C and 11D present photographs of a curling bar manufactured byAM as a green body object, and hardened in a thermal post process,respectively.

Tables 1C and 1D below present the composition of additional exemplarysub-formulations A and B, respectively.

TABLE 1C Component Wt. % Difunctional 60-80 methacrylate monomer (e.g..70-75) featuring Tg > 150° C. Secondary amine-containing  5-15 activatorfor CE curing (e.g., 5-10) Metal catalyst 0.1-0.2 Surface active agent0.01-0.1  Trifunctional acrylate 10-30 oligomer featuring Tg > (e.g.,15-25) 150° C. ( Antioxidant 0.01-0.1 

TABLE 1D Component Wt. % Cyanate ester resin 95-99 Surface active agent0.05-0.5  (e.g., 0.1-0.3) Photoinitiator 1-2 (e.g., phosphine oxidetype)

Tables 1E and 1F below present the composition of additional exemplarysub-formulations A and B, respectively.

TABLE 1E Component Wt. % Difunctional methacrylate monomer 30-50featuring Tg > 150° C. (e.g.. 35-45) Secondary amine-containing  1-10activator for CE curing Metal catalyst 0.05-0.15 Cycloaliphaticdi-functional Epoxy 30-50 resin (e.g., 35-45) Surface active agent0.01-0.1  Trifunctional acrylate oligomer 10-20 featuring Tg > 150° C.(e.g., 10-15) Antioxidant 0.01-0.1 

TABLE 1F Component Wt. % Cyanate ester resin 95-99 Surface active agent0.05-0.5  (e.g., 0.1-0.3) Photoinitiator 1-2 (e.g., phosphine oxidetype)

Example 2 Formulation Systems Comprising Acrylic Materials

An exemplary formulation system usable for printing objects in a D-ABS(core-shell) mode, as described, for example, in US Patent ApplicationPub. No. 2013/0040091 and in WO 2018/055522, which are incorporated byreference as if fully set forth herein, was first tested. Theformulation system includes two acrylic based formulations: A firstformulation that forms a reinforcer material featuring high HDT and aDLM material that forms a hardened material that features high Impactresistance and low HDT. In a core-shell D-ABS mode, the formed objectstypically have a shell made of the DLM material and a core made of thereinforcer.

FIG. 12A shows curling bar models that were printed with a reinforcerformulation known as DR-83 (RGD 537) that has an HDT of about 140° C.when hardened and a shell made of RGD515 as the DLM material. Thereinforcer formulation was a 100% reactive formulation, comprising 3-4weight percents of a photoinitiator. Significant curling and detachmentof the bars from the printing surface can be observed. The printingstopped after 4 mm due to the curling and the potential risk to theprint heads.

FIG. 12B shows the results of printing the same objects with an innercore made of a modified acrylic reinforcer formulation system thatcomprises a sub-formulation A which is similar to DR-83, and asub-formulation B which is similar to DR-83, features high HDT, butlacks a photoinitiator. The volume percents of the sub-formulations Aand B were 4% and 96%, respectively. The shell is made of RGD515. Thecurling bar model in FIG. 12B shows little to no curling.Sub-formulation B was dispensed in a layer-wise manner to form thelayer-wise patterns of the inner core and sub-formulation A was ditheredin the layer-wise patterns of the inner core.

The present inventors have designed formulations containing a polyimideprecursor such as a bismalimide, which forms a high HDT material whenhardened. These formulations are usable in 3D inkjet printing whenfurther comprising a reactive diluent, as defined herein and describedin U.S. Provisional Patent Application No. 62/610,984, filed Dec. 17,2017, the contents of which are incorporated as if fully set forthherein.

Curling bar models were printed with an exemplarybismaleimide-containing formulation which comprises BMI-689 (marketed byDesigner Molecules Inc.), about 79-80%, and cyclohexyl dimethanoldivinyl ether (about 19-20%), and 1% photoinitiator. The printing wasterminated after 3.5 mm due to significant curling that risk to theprint heads due to the curling. FIG. 13A presents the curling bar thatis obtained.

FIG. 13B shows a bar formed in accordance with some embodiments of thepresent invention. In FIG. 13B a formulation as used in FIG. 13A wasemployed as the shell having 0.3 mm thickness, and a formulation devoidof a photoinitiator was employed for forming the core. Based on thisconfiguration, no-curling was observed.

Example 3 Transparent Formulation Systems

Transparent rectangular objects were printed using reactive VeroClearreference acrylic-based formulations, comprising 1.2 and 2 weightpercents of a photoinitiator, and the same formulations when used in acore-shell configuration according to the present embodiments, whereinthe first formulation is similar to the reference formulations and formsthe outer region, and the second formulation comprises the same curablecomponents and the same photoinitiator, the latter being in an amount of0.5 and 0 weight percents. The obtained green bodies were subjected tocuring by exposure to daylight lamp for 6 hours.

FIG. 14 presents photographs of the obtained objects, showing thatobjects printed according to embodiments of the present inventionfeature reduced undesired color and improved transparency. Left objectwas printed with the reference VeroClear formulation and the rightobject was printed according to the present embodiments, using VeroClearas the outer layer, having 0.5 mm thickness, and with similarformulations having 0.5% or 0% by weight of a photoinitiator assub-formulations A and B in the inner region.

Example 4 High Throughput Printing

Objects may be manufactured with higher throughput using methodsdescribed herein. As described herein, printing a portion of the object,e.g. a core of the object with the second building material formulationprovides for reducing the temperature buildup over the AM process. Basedon the reduced temperature buildup achieved, the speed of the scanningand the throughput may be increased. Smearing of the object detailsduring the AM process may be avoided based on printing a relatively hardshell or relatively hard coating (a solidified shell or coating) thatforms an exterior of the object with the first building materialformulation as described herein. The shell or coating used for highthroughput applications may be selectively defined to be thicker thanthe shell or coatings that are used in other applications, e.g.applications for reducing curling and improving transparencies.Optionally, the shell or coating may be 0.5 mm-2 mm as opposed to 0.15mm-0.3 mm that may typically be used in other applications. In someexample embodiments, the printed object may be exposed to a posttreatment process in a high throughput printing application.Alternatively, a post treatment process is actuated.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

In addition, any priority document(s) of this application is/are herebyincorporated herein by reference in its/their entirety.

1. A method of manufacturing a three-dimensional object via additivemanufacturing (AM), the method comprising: dispensing a first buildingmaterial formulation to form an outer region, and dispensing a secondbuilding material formulation to form an inner region, the outer regionsurrounding the inner region, the inner and outer regions being shapedto form a layer of the object; and exposing the layer to a first curingcondition, wherein the first and the second building materialformulations and the first curing condition are selected such that uponthe exposing, the first building material formulation is hardened to ahigher degree than the second building formulation; repeating thedispensing and the exposing to the first curing condition tosequentially form a plurality of layers of the object, wherein the outerregions form a hardened coating that at least partially encapsulates theinner regions; and collectively exposing the plurality of layers to asecond curing condition, wherein the second curing condition is otherthan the first curing condition and wherein the second curing conditionis selected to increase the degree that the inner region is hardened;wherein the first building material formulation comprises a firstcurable material and an initiator for promoting hardening of the firstcurable material, and wherein the initiator is active towards promotingthe hardening upon exposure to the first curing condition.
 2. The methodof claim 1, wherein the first and second building material formulationsand said first curing condition are selected such that upon the exposingto the first curing condition, a change in a hardening parameter of thefirst formulation is higher than a change in a hardening parameter ofthe second formulation by at least 2-folds.
 3. The method of claim 2,wherein said hardening parameter is viscosity and/or loss tangent. 4.The method of claim 1, wherein the first and second building materialformulations and said first curing condition are selected such that uponthe exposing to said first curing condition, a hardening kineticparameter of the first formulation is higher than a hardening kineticparameter of the second formulation by at least 2-folds.
 5. The methodof claim 4, wherein said hardening kinetic parameter is a rate of achange in a viscosity or a rate of a change in a loss tangent.
 6. Themethod of claim 1, wherein the first and the second building materialformulations and the first curing condition are selected such that uponsaid exposing to the first curing condition, a hardening degree of saidfirst building material formulation is at least 70% and a hardeningdegree of said second building material formulation is no more than 50%.7. The method of claim 1, wherein the second building materialformulation comprises a second curable material and at least one of thefirst and the second building material formulations comprises aninitiator for promoting hardening of the second curable material, andwherein the initiator is inactive or is partially active towards thehardening upon exposure to the first curing condition.
 8. The method ofclaim 7, wherein a total amount of the initiator in the at least one ofthe first and second building material formulations is less than 50%, orless than 30%, by weight, of an amount of the initiator required forpromoting hardening of at least 70% of the second curable material uponexposure to the first curing condition.
 9. The method of claim 8,wherein the second building material formulation comprises at least twosub-formulations A and B, each comprising the second curable material,wherein an amount of the initiator in sub-formulation A is higher by atleast 100% of an amount of the initiator in sub-formulation B, andwherein a weight ratio of sub-formulations A and B is lower than 0.5.10. The method of claim 9, wherein dispensing the second buildingformulation is such that the sub-formulation A is dithered within theinner region.
 11. (canceled)
 12. The method of claim 1, wherein thefirst curing condition comprises irradiation.
 13. The method of claim12, wherein the irradiation is UV-irradiation.
 14. The method of claim13, wherein the first building material formulation comprises a firstcurable material which is a UV curable material, and a photo-initiatorin an amount sufficient for promoting hardening of at least 70% of thefirst building material formulation upon exposure to said first curingcondition.
 15. The method of claim 13, wherein the second buildingmaterial formulation comprises a second curable material which is a UVcurable material, and a photo-initiator in an amount that promoteshardening of no more than 50% of the second building materialformulation upon exposure to the first curing condition.
 16. The methodof claim 13, wherein the second building material formulation hardensupon exposure to a heat.
 17. The method of claim 1, wherein at least oneof the first and second building material formulations provides atransparent hardened material.
 18. The method of claim 1, wherein thesecond building material formulation comprises a second curable materialfeaturing, when hardened, at least one of: a heat distortion temperature(HDT) above a steady state temperature of the plurality of layers duringthe AM process; a glass transition temperature (Tg) above a steady statetemperature of the plurality of layers during the AM process; a heatdistortion temperature (HDT) above 70° C.; and a glass transitiontemperature (Tg) above 70° C. 19-21. (canceled)
 22. The method of claim1, wherein the first building material formulation comprises a firstcurable material featuring, when hardened, at least one of: a heatdistortion temperature (HDT) below a steady state temperature of theplurality of layers during the AM process; a glass transitiontemperature (Tg) below a steady state temperature of the plurality oflayers during the AM process; a heat distortion temperature (HDT) below70° C.; and a glass transition temperature (Tg) below 70° C. 23-25.(canceled)
 26. The method of claim 1, wherein the coating is configuredto have a thickness that is less than 1 mm.
 27. (canceled)